Google's HTTP/2 codec slows Envoy

Google's oghttp2 HTTP/2 codec, which became Envoy's default in version 1.34, causes a 15-25% reduction in throughput compared to the previous nghttp2 codec, with the performance gap traced to inefficient header decompression. The regression was significant enough that Envoy reverted to nghttp2 as the default in v1.37.0, though the underlying performance issues with oghttp2's header decompression remain unresolved.