Why?

C++ natively supports unsigned integer types (uint8_t, uint16_t, uint32_t, uint64_t) which are widely used in systems programming. This PR adds serialization support for these types in native mode (xlang=false), following the same pattern as the Rust implementation.

What does this PR do?

1. Adds unsigned TypeIds to cpp/fory/type/type.h:

   • U8 = 64, U16 = 65, U32 = 66, U64 = 67 for basic unsigned types
   • U16_ARRAY = 73, U32_ARRAY = 74, U64_ARRAY = 75 for unsigned arrays

2. Implements unsigned type serializers in cpp/fory/serialization/unsigned_serializer.h:

   • Basic types: uint8_t, uint16_t, uint32_t, uint64_t
   • Fixed-size arrays: std::array<uintN_t, N>
   • Vectors: std::vector<uintN_t>

3. Updates struct serializer to recognize unsigned types as primitive types, enabling efficient serialization of structs with unsigned fields.

4. Adds comprehensive tests covering:

   • Primitive unsigned type roundtrips
   • Unsigned vector and array roundtrips
   • Structs with unsigned fields
   • Boundary value tests
   • TypeId verification

Note: Unsigned types are only supported in native mode (xlang=false). This follows the xlang specification which does not include unsigned types for cross-language compatibility.

Related issues

#2906

Does this PR introduce any user-facing change?

Yes - users can now serialize/deserialize unsigned integer types in C++ when using native mode.

• Does this PR introduce any public API change?
• Does this PR introduce any binary protocol compatibility change?

Benchmark

N/A - This is a new feature addition, not a performance optimization.