Cache executor metadata from initialization (#40343)

## What changed

- Include `environmentInfo` in the exec-server `initialize` response and seed the Rust client's metadata cache from it.
- Fall back to one lazy `environment/info` request when connecting to older servers that omit initialization metadata, then share the cached result across client clones and session recovery.
- Keep app-server `environment/info` requests uncached so they continue to probe the executor.

## Testing

- Cover initialization metadata, the legacy-server fallback, shared caching, accepted WebSocket environments, and repeated uncached app-server probes.

GitOrigin-RevId: 380132d9db183998d73e8c6b0954e4d70c7e8406

codex-rs/rmcp-client/tests/streamable_http_remote.rs

@@ -124,7 +124,7 @@ async fn stalled_handshake_unblocks_remote_executor(
 
     tokio::time::timeout(
         Duration::from_secs(2),
-        exec_server.client.environment_info(),
+        exec_server.client.environment_status(),
     )
     .await
     .context("a timed-out handshake must not leave the serial executor blocked")??;