Implement Java 1.4 regular expression APIs

[dlunch]

Summary

• add java.lang.CharSequence and integrate it with String and StringBuffer
• implement Java 1.4 java.util.regex.Pattern, Matcher, and PatternSyntaxException
• add String.matches, replaceFirst, replaceAll, and both split overloads through the regex APIs
• use regex 1.13.1 directly without translating historical Java regex syntax

Behavior

Matcher state, captures, replacement expansion, split limits, and public offsets follow the Java 1.4 API shape. Rust byte offsets are converted to Java UTF-16 indices. Full matches use an internal anchored wrapper, with a fallback for terminal extended-mode comments while preserving the original pattern source.

Validation

• cargo test --workspace --quiet (504 passed, 1 existing ignored)
• cargo test -p java_runtime regex (45 passed)
• cargo check -p java_runtime --lib
• cargo fmt --all -- --check
• cargo clippy -p java_runtime --lib --tests -- -D warnings

[codecov]

Codecov Report

❌ Patch coverage is 99.42474% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.77%. Comparing base (1d26040) to head (0281488).

Files with missing lines	Patch %	Lines
...ava_runtime/src/classes/java/util/regex/matcher.rs	98.78%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #193      +/-   ##
==========================================
+ Coverage   90.49%   90.77%   +0.27%     
==========================================
  Files         265      269       +4     
  Lines       32349    33390    +1041     
==========================================
+ Hits        29275    30310    +1035     
- Misses       3074     3080       +6     

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[Copilot]

Pull request overview

This PR adds Java 1.4-compatible regular expression APIs to the java_runtime crate, introducing java.lang.CharSequence support and implementing java.util.regex.Pattern, Matcher, and PatternSyntaxException, plus String convenience methods that route through the regex API.

Changes:

• Add java/lang/CharSequence and implement/integrate it with String and StringBuffer (incl. subSequence behavior).
• Implement java/util/regex core classes (Pattern, Matcher, PatternSyntaxException) backed by Rust regex.
• Add comprehensive runtime-level tests for matcher state, replacements, split semantics, flag validation, and exception formatting.

Reviewed changes

Copilot reviewed 20 out of 21 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
java_runtime/tests/classes/java/util/regex/test_split.rs	Adds tests for Pattern.split (limits, UTF-16 boundaries, null handling).
java_runtime/tests/classes/java/util/regex/test_replacement.rs	Adds tests for Matcher replacement APIs (appendReplacement, appendTail, replaceAll/First) and exception ordering.
java_runtime/tests/classes/java/util/regex/test_pattern.rs	Adds tests for Pattern surface, flags validation, pass-through syntax, and null handling.
java_runtime/tests/classes/java/util/regex/test_pattern_syntax_exception.rs	Adds tests for PatternSyntaxException API contract and message formatting behavior.
java_runtime/tests/classes/java/util/regex/test_matcher.rs	Adds extensive tests for Matcher state machine, UTF-16 offsets, snapshot behavior, and error ordering.
java_runtime/tests/classes/java/util/regex/mod.rs	Wires regex test modules into the test tree.
java_runtime/tests/classes/java/util/mod.rs	Registers the new regex test module under java/util.
java_runtime/tests/classes/java/lang/test_string.rs	Adds tests for CharSequence integration and String regex convenience methods.
java_runtime/tests/classes/java/lang/test_string_buffer.rs	Adds tests for StringBuffer CharSequence behavior and snapshot semantics.
java_runtime/src/loader.rs	Registers CharSequence and the new java.util.regex runtime classes.
java_runtime/src/classes/java/util/regex/pattern.rs	Implements java.util.regex.Pattern including compile, matches, split, and flag mapping into Rust regex.
java_runtime/src/classes/java/util/regex/matcher.rs	Implements java.util.regex.Matcher including match/search state, capture offsets, and replacement expansion.
java_runtime/src/classes/java/util/regex/pattern_syntax_exception.rs	Implements java.util.regex.PatternSyntaxException and Java 1.4-style message formatting.
java_runtime/src/classes/java/util/regex.rs	Adds the java_runtime::classes::java::util::regex module and exports.
java_runtime/src/classes/java/util.rs	Exposes the new regex module under java.util.
java_runtime/src/classes/java/lang/string.rs	Makes String implement CharSequence and adds regex convenience methods (matches, replaceFirst/All, split).
java_runtime/src/classes/java/lang/string_buffer.rs	Makes StringBuffer implement CharSequence and adds subSequence.
java_runtime/src/classes/java/lang/char_sequence.rs	Adds the java.lang.CharSequence interface definition.
java_runtime/src/classes/java/lang.rs	Registers/exports CharSequence from java.lang.
java_runtime/Cargo.toml	Adds the regex dependency for the runtime implementation.
Cargo.lock	Locks regex and related dependency versions.

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