feat(dart): add bfloat16 and bfloat16_array support

[miantalha45]

Summary

• Add BFloat16 type class with IEEE 754 bfloat16 conversions (round-to-nearest, ties-to-even).
• Add bfloat16 (type ID 18) and bfloat16_array (type ID 54) to the Dart type system, serializers, buffer, codegen, and type resolver
• Add 22 tests covering scalar conversions (±0, ±Inf, NaN, subnormals, min/max normal), rounding, equality, buffer round-trips, and packed array serialization

Changes

File	Change
lib/src/types/bfloat16.dart	New BFloat16 class with fromBits, fromFloat32, toBits, toDouble
lib/src/buffer.dart	writeBfloat16() / readBfloat16()
lib/src/resolver/type_resolver.dart	TypeIds.bfloat16=18, TypeIds.bfloat16Array=54, all resolution paths
lib/src/serializer/primitive_serializers.dart	bfloat16Serializer constant, write/read cases
lib/src/codegen/fory_generator.dart	All codegen paths for bfloat16/bfloat16_array
lib/src/codegen/generated_support.dart	Cursor writeBfloat16() / readBfloat16()
lib/src/context/write_context.dart	writeBfloat16() method
lib/src/context/read_context.dart	readBfloat16() method
lib/src/meta/type_meta.dart	Wire type checks for bfloat16/bfloat16Array
lib/fory.dart	Public export of bfloat16.dart
test/bfloat16_test.dart	22 tests

Test plan

• All 22 new bfloat16 tests pass (dart test test/bfloat16_test.dart)
• All existing tests still pass (dart test)
• dart analyze clean (only pre-existing issues)

AI Assistance Checklist

• Substantial AI assistance was used in this PR (yes)
• I included the standardized AI Usage Disclosure block below
• I can explain and defend all important changes without AI help
• I reviewed AI-assisted code changes line by line before submission
• I ran adequate human verification and recorded evidence (local/CI checks, pass/fail summary, and review confirmation)
• I added/updated tests and specs where required
• I validated protocol/performance impacts with evidence when applicable
• I verified licensing and provenance compliance

AI Usage Disclosure

• substantial_ai_assistance: yes
• scope: <design drafting | code drafting>

AI Review Comments

Claude Code:

Skill Review

The implementation is correct and complete. Type IDs match the spec (18/54), conversion logic matches the JS reference exactly, all codegen/resolver/serializer/context/cursor paths are covered, and all 31 tests pass (22 new + 9 existing).

General Review

The investigation found 3 critical missing changes and 1 design gap: generated_support.dart - Missing writeBfloat16() / readBfloat16() on cursors (codegen will fail) write_context.dart - Missing writeBfloat16() read_context.dart - Missing readBfloat16() These are now all fixed.

Fixes #3287

[chaokunyang]

where is ai review comments?

[miantalha45]

Adding AI Review comments

[miantalha45]

where is ai review comments?

Added