feat: support proxy for ws connection (#9409)

unfortunately tokio-tungstenite doesn't support proxy configuration
outbox, while https://github.com/snapview/tokio-tungstenite/pull/370 is
in review, we can depend on source code for now.

codex-rs/core/tests/common/responses.rs

@@ -923,7 +923,7 @@ pub async fn start_websocket_server_with_headers(
                     let Ok(payload) = serde_json::to_string(event) else {
                         continue;
                     };
-                    if ws_stream.send(Message::Text(payload)).await.is_err() {
+                    if ws_stream.send(Message::Text(payload.into())).await.is_err() {
                         break;
                     }
                 }