Enable zstd compression for code-mode gRPC responses (#57212)

## What changed

- Configure the code-mode host to send zstd-compressed responses when clients advertise support, and enable both client transports to accept them.
- Preserve uncompressed responses for clients that do not advertise zstd support.
- Patch `tonic` in Bazel builds to use zstd compression level 1, favoring response latency over compression ratio.

## Testing

Extend the TCP session integration test to check response encoding and successful session opening for both zstd-capable and uncompressed-only clients.

GitOrigin-RevId: b6cf0da51dd30fc2ac9a1b0af11bec26555c559d

codex-rs/code-mode/src/grpc_session/transport.rs

@@ -42,6 +42,7 @@ impl SharedTransport {
         let transport = channel.map_err(|error| Status::from_error(Box::new(error)));
         Self::Connected(
             CodeModeHostClient::new(BoxCloneSyncService::new(transport))
+                .accept_compressed(tonic::codec::CompressionEncoding::Zstd)
                 .max_decoding_message_size(MAX_FRAME_BYTES)
                 .max_encoding_message_size(MAX_FRAME_BYTES),
         )
@@ -132,6 +133,7 @@ impl SharedTransport {
             CodeModeHostClient::with_origin(BoxCloneSyncService::new(transport), origin)
         };
         let client = client
+            .accept_compressed(tonic::codec::CompressionEncoding::Zstd)
             .max_decoding_message_size(MAX_FRAME_BYTES)
             .max_encoding_message_size(MAX_FRAME_BYTES);
         *cached = Some((bound_factory, client.clone()));