Fix an inconsistency in the Node generator. Bytes arguments were lowered as raw byte arrays even when the emitted ffi-rs signature expected a UniffiRustBufferStruct.

The patch updates Type::Bytes to use the same RustBuffer-backed lower/lift path as other serialized types like String, Map, Sequence, Enum, and Record. That means generated bindings now:

• lower byte arguments into UniffiRustBufferValue.allocateWithBytes(...).toStruct() before the FFI call
• lift byte return values from the RustBuffer returned by FFI
• use FfiConverterArrayBuffer consistently for bytes

This brings the generated call-site representation back in line with the generated FFI signatures and removes the need for downstream post-generation patches.

Added a generator regression test covering bytes round_trip(bytes input), and the current Rust test suite passes.

Fixes #30
Fixes #31