Cap gRPC reflection response buffering

[ryanfowler]

Summary

• Added reflection-specific limits to framed gRPC body collection so discovery responses cannot grow without bound from many small valid frames.
• Applied a 128-message and 64 MiB decoded-byte cap to gRPC reflection reads, with clear errors when either limit is exceeded.
• Added regression coverage for the hostile reflection case that overflows the message-count limit.

Testing

• cargo fmt
• cargo clippy --locked --all-targets --all-features -- -D warnings
• cargo test --all-features grpc::body::tests
• cargo test --all-features --test grpc grpc_reflection_rejects_too_many_framed_messages -- --test-threads=1