test: add gRPC compression integration tests

Add comprehensive tests verifying native gRPC compression works
correctly between consumer and provider:

- TestGRPCCompressionEnabled: verifies data is compressed (99%+ reduction)
- TestGRPCCompressionDisabled: verifies no compression without flag
- TestGRPCCompressionBidirectional: verifies both request and response compression
- TestGRPCCompressionWithConnectGRPCClient: tests via actual ConnectGRPCClient function
- TestGRPCCompressionSmallPayload: verifies small payload handling
- BenchmarkGRPCWithCompression/WithoutCompression: performance comparison

Uses gRPC stats handler to measure actual wire vs logical payload sizes.

Author: nimrod-teich