Add gzip compression tests

[sullis]

Summary

Adds integration tests to verify gzip compression support for gRPC requests and responses.

Changes

• GrpcGzipCompressionTest — new test class that:
  • Registers a server-side interceptor (via @GRpcGlobalInterceptor) that captures the incoming grpc-encoding header and enables gzip compression on responses
  • gzipCompressedRequestShouldSucceed — sends a gzip-compressed request using withCompression("gzip") and asserts the server received the grpc-encoding: gzip header
  • gzipCompressedResponseShouldBeDecodable — sends a gzip-compressed request, captures the response grpc-encoding header via a client interceptor, and asserts the response was also gzip-encoded

[sullis]

ready for review