Implement Java 5 Formatter support

[dlunch]

Summary

• add Java 5 Formatter, Formattable, formatting exceptions, and common conversions
• add the supporting Appendable, Closeable, Flushable, StringBuilder, and Enum APIs
• integrate String.format, PrintStream.format/printf, and PrintWriter.format/printf
• match Java 5 public class hierarchy, flags, fields, constructors, and public method descriptors with manifest tests

Compatibility scope

This provides the practical Java 5 formatting subset used by typical applications. Date/time (%t/%T), hexadecimal floating point (%a/%A), arbitrary-precision number formatting, and non-English locale localization remain out of scope.

Validation

• cargo test --workspace --quiet (524 passed, 1 pre-existing ignored)
• cargo clippy --workspace --all-targets -- -D warnings
• cargo fmt --all -- --check
• git diff --check

[codecov]

Codecov Report

❌ Patch coverage is 64.96701% with 1752 lines in your changes missing coverage. Please review.
✅ Project coverage is 87.41%. Comparing base (f6cab40) to head (9f05da0).

Files with missing lines	Patch %	Lines
...e/src/classes/java/lang/abstract_string_builder.rs	36.17%	591 Missing ⚠️
...va_runtime/src/classes/java/lang/string_builder.rs	46.84%	488 Missing ⚠️
java_runtime/src/classes/java/util/formatter.rs	79.39%	230 Missing ⚠️
...ava_runtime/src/classes/java/lang/string_buffer.rs	59.48%	205 Missing ⚠️
java_runtime/src/classes/java/io/print_writer.rs	70.28%	82 Missing ⚠️
java_runtime/src/classes/java/io/print_stream.rs	77.85%	60 Missing ⚠️
java_runtime/src/classes/java/lang/enum.rs	62.75%	54 Missing ⚠️
java_runtime/src/classes/java/lang/string.rs	61.70%	18 Missing ⚠️
...runtime/src/classes/java/util/formattable_flags.rs	78.37%	8 Missing ⚠️
java_runtime/src/classes/java/lang/byte.rs	66.66%	3 Missing ⚠️
... and 5 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #196      +/-   ##
==========================================
- Coverage   90.77%   87.41%   -3.37%     
==========================================
  Files         269      292      +23     
  Lines       33392    38301    +4909     
==========================================
+ Hits        30312    33479    +3167     
- Misses       3080     4822    +1742     

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[Copilot]

Pull request overview

This PR implements a Java 5–compatible formatting stack in RustJava, adding java.util.Formatter/Formattable plus the supporting Appendable/Closeable/Flushable/StringBuilder/Enum APIs, and wiring formatting entrypoints like String.format and PrintStream/PrintWriter format/printf. It also expands the runtime class registry and updates conformance/integration tests to validate Java 5 public API shapes and key formatting behaviors.

Changes:

• Add java.util.Formatter + formatting exceptions and a small integration fixture under test_data/ to validate end-to-end formatting/output behavior.
• Introduce Java 5 IO/lang support types (Appendable, Closeable, Flushable, AbstractStringBuilder, StringBuilder, Enum) and integrate them into PrintStream, PrintWriter, and String.
• Update/extend Rust tests to assert Java 5 descriptors, access flags, bridges, and selected behavioral contracts (autoboxing valueOf, formatting IO behaviors, etc.).

Reviewed changes

Copilot reviewed 53 out of 57 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
test_data/src/FormatterIntegration.java	New Java integration program exercising Formatter, Formattable, Appendable, and stream/writer formatting.
test_data/FormatterIntegration.txt	Expected output for the new formatter integration fixture.
java_runtime/tests/classes/java/util/mod.rs	Registers the new test_formatter module in util test suite.
java_runtime/tests/classes/java/util/test_formatter.rs	Adds API-shape and behavior tests for Formatter, formatting exceptions, Enum, and IO type bridges.
java_runtime/tests/classes/java/lang/mod.rs	Registers new test_string_builder module in lang test suite.
java_runtime/tests/classes/java/lang/test_string_builder.rs	New tests for Appendable and Java 5 StringBuilder hierarchy/bridges and UTF-16 behavior.
java_runtime/tests/classes/java/lang/test_string_buffer.rs	Updates expectations for StringBuffer hierarchy and method flags/descriptors.
java_runtime/tests/classes/java/lang/test_character.rs	Updates Character.valueOf(char) expectation for Java 5.
java_runtime/tests/classes/java/lang/test_boolean.rs	Updates Boolean.valueOf(boolean) expectation for Java 5 interning semantics.
java_runtime/tests/classes/java/io/test_print_writer.rs	Extends PrintWriter API surface checks (constructors + format/printf + append bridges + setError).
java_runtime/tests/classes/java/io/test_print_stream.rs	Extends PrintStream API surface checks and adds an autoFlush + format flush behavior assertion.
java_runtime/tests/classes/java/io/test_file_reader_writer.rs	Adds a regression test ensuring Formatter file constructors truncate before writing.
java_runtime/src/loader.rs	Registers new runtime class protos for formatter-related and supporting Java 5 classes.
java_runtime/src/classes/java/util.rs	Adds modules/exports for Formatter, exceptions, Formattable, and related types.
java_runtime/src/classes/java/util/formatter.rs	Core java.util.Formatter implementation and formatting engine.
java_runtime/src/classes/java/util/formattable.rs	Adds the java.util.Formattable interface proto.
java_runtime/src/classes/java/util/formattable_flags.rs	Adds java.util.FormattableFlags constants holder.
java_runtime/src/classes/java/util/formatter_closed_exception.rs	Adds FormatterClosedException.
java_runtime/src/classes/java/util/formatter_big_decimal_layout_form.rs	Adds Formatter$BigDecimalLayoutForm enum support for signature compatibility.
java_runtime/src/classes/java/util/illegal_format_exception.rs	Adds base IllegalFormatException.
java_runtime/src/classes/java/util/duplicate_format_flags_exception.rs	Adds DuplicateFormatFlagsException.
java_runtime/src/classes/java/util/illegal_format_flags_exception.rs	Adds IllegalFormatFlagsException.
java_runtime/src/classes/java/util/format_flags_conversion_mismatch_exception.rs	Adds FormatFlagsConversionMismatchException.
java_runtime/src/classes/java/util/illegal_format_conversion_exception.rs	Adds IllegalFormatConversionException.
java_runtime/src/classes/java/util/illegal_format_code_point_exception.rs	Adds IllegalFormatCodePointException.
java_runtime/src/classes/java/util/illegal_format_precision_exception.rs	Adds IllegalFormatPrecisionException.
java_runtime/src/classes/java/util/illegal_format_width_exception.rs	Adds IllegalFormatWidthException.
java_runtime/src/classes/java/util/missing_format_argument_exception.rs	Adds MissingFormatArgumentException.
java_runtime/src/classes/java/util/missing_format_width_exception.rs	Adds MissingFormatWidthException.
java_runtime/src/classes/java/util/unknown_format_conversion_exception.rs	Adds UnknownFormatConversionException.
java_runtime/src/classes/java/util/unknown_format_flags_exception.rs	Adds UnknownFormatFlagsException.
java_runtime/src/classes/java/lang.rs	Wires new Java 5 lang modules into the runtime (Appendable, AbstractStringBuilder, Enum, StringBuilder).
java_runtime/src/classes/java/lang/appendable.rs	Adds the java.lang.Appendable interface proto.
java_runtime/src/classes/java/lang/abstract_string_builder.rs	Adds AbstractStringBuilder implementation used by both StringBuffer and StringBuilder.
java_runtime/src/classes/java/lang/string_builder.rs	Adds StringBuilder implementation and bridge methods.
java_runtime/src/classes/java/lang/string_buffer.rs	Refactors StringBuffer to extend AbstractStringBuilder and adds Java 5 overloads/bridges.
java_runtime/src/classes/java/lang/enum.rs	Adds java.lang.Enum base implementation and Enum.valueOf.
java_runtime/src/classes/java/lang/string.rs	Adds String.format(...) overloads backed by Formatter.
java_runtime/src/classes/java/lang/boolean.rs	Adds Boolean.valueOf(boolean) returning interned constants.
java_runtime/src/classes/java/lang/byte.rs	Adds Byte.valueOf(byte).
java_runtime/src/classes/java/lang/character.rs	Adds Character.valueOf(char).
java_runtime/src/classes/java/lang/double.rs	Adds Double.valueOf(double).
java_runtime/src/classes/java/lang/float.rs	Adds Float.valueOf(float).
java_runtime/src/classes/java/lang/long.rs	Adds Long.valueOf(long).
java_runtime/src/classes/java/lang/short.rs	Adds Short.valueOf(short).
java_runtime/src/classes/java/io.rs	Exposes Closeable and Flushable in the java.io module exports.
java_runtime/src/classes/java/io/closeable.rs	Adds the java.io.Closeable interface proto.
java_runtime/src/classes/java/io/flushable.rs	Adds the java.io.Flushable interface proto.
java_runtime/src/classes/java/io/output_stream.rs	Updates OutputStream to implement Closeable/Flushable and fixes public/abstract method flags.
java_runtime/src/classes/java/io/writer.rs	Updates Writer to implement Appendable/Closeable/Flushable and adds append(...) methods + bridges.
java_runtime/src/classes/java/io/output_stream_writer.rs	Refactors encoding validation and reuse across new constructors/callers.
java_runtime/src/classes/java/io/print_stream.rs	Adds PrintStream.format/printf, Appendable bridges, and new constructors.
java_runtime/src/classes/java/io/print_writer.rs	Adds PrintWriter.format/printf, Appendable bridges, and new constructors.

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