Add optional process metrics sampling for code-mode hosts (#57841)

## What changed

- Add `GetProcessMetrics` and provider sampling APIs for process ID, start time, cumulative CPU time, and resident memory, exposed through `ThreadManager` without creating a thread or session.
- Distinguish unsupported collection, a locally absent host, and sampling failures. Process-owned providers never start or replace a host when sampling.
- Bound gRPC sampling to one second without retries or explicit connection resets. Run optional collectors on a detached worker with at most one collection in flight, so stalled collection cannot block the HTTP/2 driver or runtime shutdown.

## Testing

Add coverage for snapshots, collector errors and panics, deadlines, overload, and shutdown with a stuck collector. Extend lifecycle tests to check that sampling preserves session state and keepalive behavior without starting or restarting local hosts.

GitOrigin-RevId: eeafe275891d0464636f28a29345a87aed1a12dc

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

@@ -15,11 +15,13 @@ enum ListenTransport {
     Grpc(SocketAddr),
 }
 
-pub(crate) async fn run_transport(listen_url: &str) -> Result<()> {
+pub(crate) async fn run_transport(listen_url: &str, host: crate::GrpcCodeModeHost) -> Result<()> {
     match parse_listen_url(listen_url)? {
         ListenTransport::Stdio => crate::run_stdio().await,
-        ListenTransport::GrpcStdio => crate::grpc_stdio::run().await,
-        ListenTransport::Grpc(bind_address) => grpc_transport::run_tcp_listener(bind_address).await,
+        ListenTransport::GrpcStdio => crate::grpc_stdio::run(host).await,
+        ListenTransport::Grpc(bind_address) => {
+            grpc_transport::run_tcp_listener(bind_address, host).await
+        }
     }
 }