feat(dart): add float16 to dart

[ayush00git]

Why?

As requested in Issue #3209, Dart implementation was missing support for IEEE 754 half-precision floating-point (Float16) types that are already available in other Fory language implementations (Rust, Go, C++, Python). This PR adds complete Float16 support for Dart.

What does this PR do?

This PR implements schema-based support for IEEE 754 Float16 types in the Fory Dart library:

Added Types

• float16

Changes Made

1. lib/src/datatype/float16.dart

Implemented the Float16 class which wraps a 16-bit integer and handles IEEE 754 conversions (handling rounding, subnormals, signed zeros, NaN/Infinity):

final class Float16 extends FixedNum {
  final int _bits;
  // ...
  factory Float16(num value) => Float16.fromDouble(value.toDouble());
  double toDouble() => _bitsToDouble(_bits);
}

2. lib/src/memory/

Added read/write support for 16-bit floats in ByteReader and ByteWriter:

void writeFloat16(Float16 value);
Float16 readFloat16();

3. lib/src/serializer/

Registered Float16Serializer to handle serialization of Float16 types in PrimitiveTypeSerializer:

typeToTypeInfo[Float16]!.serializer = Float16Serializer.cache.getSerializer(conf);

4. lib/src/const/dart_type.dart

Added FLOAT16 to DartTypeEnum for type inference and registry.

5. test/cross_lang_test/

Updated cross-language tests to fix lint issues and build errors:

• Renamed enum constants in xlang_test_defs.dart and xlang_test_main.dart to follow Dart's lowerCamelCase convention (e.g., VALUE_A -> valueA).

Usage Example

import 'package:fory/src/datatype/float16.dart'; 
import 'package:fory/src/memory/byte_writer.dart';

var val = Float16(1.5);
print(val.toDouble())

// Handling limits and edge cases
var max = Float16(65504.0);
var inf = Float16(65505.0);
var subnormal = Float16(0.0000000596046);

// Serialization
var bw = ByteWriter();
bw.writeFloat16(val);

Related issues

• Closes [Dart] add float16 to dart #3209

Does this PR introduce any user-facing change?

• Does this PR introduce any public API change?

  • Yes: Adds Float16 class and corresponding NumType.float16.
  • Yes: Adds readFloat16 / writeFloat16 to memory interfaces.
  • Yes: Exports Float16 for user consumption.

• Does this PR introduce any binary protocol compatibility change?

  • Yes: Adds support for TypeId 17 (Float16).
  • Cross-language compatible: Uses the same TypeId values as other Fory implementations.

Benchmark

N/A

[ayush00git]

Hey @chaokunyang
Have a look at the implementation and let me know your reviews

[chaokunyang]

@ayush00git I removed dart/packages/fory-test/test/cross_lang_test/xlang_test_defs.dart, could you address conflict?

[ayush00git]

@ayush00git I removed dart/packages/fory-test/test/cross_lang_test/xlang_test_defs.dart, could you address conflict?

Hii @chaokunyang
Have a look and let me know

[chaokunyang]

LGTM