fix(grpc): read access log status from response trailers

Closes #19.

The access log was reading grpc-status from response headers, so RPCs that sent their status in trailers were logged as OK even when they failed.

This wraps the response body to capture the trailer status and log when the stream finishes. If the body is dropped before a status arrives, it logs Unknown. Header-only responses still work, and each response gets one access log.

The first commit records the existing behavior with a passing test; the second adds the fix and updates the assertions.

Verified with gRPC unit and integration tests, formatting, and clippy. I also checked trailer responses, header-only responses, and client resets through Tonic/HTTP2 in a temporary test crate.

Continues !145 (closed) from the community fork.