Add language bindings for buffer-backed sequences

[yuanknv]

Summary

• expose exception-safe C helpers for creating, cloning, querying, comparing, and destroying rosidl::Buffer<uint8_t>
• make primitive sequence copy and equality operations preserve native Buffer ownership
• keep string and wide-string sequences on their existing three-field ABI

Dependency

Foundation PR for the Rust native Buffer stack; no other draft in the stack is required to review this change.

Test plan

• Build rosidl_buffer and rosidl_runtime_c
• Run their C/C++ unit tests
• Validate Buffer-backed sequence clone, equality, and cleanup