[BugFix] Fix ASAN crash for BOOLEAN nested in Avro complex-type columns (backport #76041)

[mergify]

Why I'm doing:

Fix the daily ASAN crash reported in StarRocks/StarRocksTest#11522:

be/src/gutil/casts.h:78: To down_cast(From*) [with To = FixedLengthColumn<signed char>*; ...]:
Assertion `f == __null || dynamic_cast<To>(f) != __null' failed.

It aborts BE when an Avro routine load targets a native complex-type column (STRUCT/MAP/ARRAY) that contains a BOOLEAN field/element/value.

What I'm doing:

BooleanColumn is FixedLengthColumn<uint8_t>, but the nested (non-adaptive) add_nullable_column in be/src/formats/avro/nullable_column.cpp dispatched TYPE_BOOLEAN through add_nullable_numeric_column<int8_t>. add_numeric_column<int8_t> then down_casts the uint8 column to FixedLengthColumn<int8_t>*, which trips the dynamic_cast assert under ASAN/DEBUG.

The adaptive path (add_adpative_nullable_column, used for top-level columns) already dispatched TYPE_BOOLEAN through the correct <uint8_t> — which is why only complex types crashed and a plain top-level BOOLEAN column was fine. The fix dispatches the nested path through <uint8_t> too. add_numeric_column<uint8_t> is already explicitly instantiated, so no other change is needed.

Added regression test AvroScannerTest.test_struct_with_boolean; the full AvroScannerTest suite (26 tests) passes on a clean ASAN build.

Notes:

• The crash-reachable STRUCT/MAP paths were made reachable by [Enhancement] Support native MAP/STRUCT target columns for Avro routine load #74901 (main only). The nested ARRAY path carries the same latent mismatch since [Feature] Parse avro data directly #19866.
• In opt builds the assert is compiled out and int8_t/uint8_t are layout-identical, so for valid boolean data this is an ASAN/DEBUG crash rather than a release data-correctness issue.

Fixes StarRocks/StarRocksTest#11522

What type of PR is this:

• BugFix
• Feature
• Enhancement
• Refactor
• UT
• Doc
• Tool

Does this PR entail a change in behavior?

• Yes, this PR will result in a change in behavior.
• No, this PR will not result in a change in behavior.

Checklist:

• I have added test cases for my bug fix or my new feature
• This pr needs user documentation (for new or modified features or behaviors)
  • I have added documentation for my new feature or new function
  • This pr needs auto generate documentation
• This is a backport pr

Bugfix cherry-pick branch check:

• I have checked the version labels which the pr will be auto-backported to the target branch
  • 4.1
  • 4.0
  • 3.5

---

This is an automatic backport of pull request #76041 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of bed4395 has failed:

On branch mergify/bp/branch-4.0/pr-76041
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Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   be/src/formats/avro/nullable_column.cpp
	both modified:   be/test/exec/avro_scanner_test.cpp

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[mergify]

@mergify[bot]: Backport conflict, please reslove the conflict and resubmit the pr