Add integration coverage for streaming NDJSON, gRPC trailers, and WebSockets

[ryanfowler]

Summary

• Add an h2c gRPC test server that exercises multi-frame responses and non-OK grpc-status trailers.
• Add streaming NDJSON coverage for both buffered formatting and live stdout streaming while the response is still open.
• Add a WebSocket push server test that validates handshake query/header handling and mixed text/binary message delivery.

Testing

• cargo fmt
• cargo clippy --locked --all-targets --all-features -- -D warnings
• cargo test --all-features
• cargo test --all-features --test integration -- --test-threads=1