Enable coordinated MCP OAuth refresh (#42413)

## What changed

- Honor `McpOAuthRefreshMode::Coordinated` for streamable HTTP MCP connections by letting RMCP refresh and persist credentials through the pinned credential store.
- Reread credentials while holding the refresh lock, persist refreshed tokens before retrying requests, and serialize login and logout writes with in-flight refreshes.
- Keep OAuth preparation outside MCP operation and handshake deadlines, and allow refresh persistence to finish if the initiating caller is cancelled.

## Testing

- Cover coordinated startup refresh, concurrent refreshes, `401` retries, credential mutation races, provider timeouts, and caller cancellation.

GitOrigin-RevId: 100ae788048087be23e26bb43f868b1fcebb007a

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

@@ -105,10 +105,17 @@ pub(crate) async fn create_client_with_http_client(
 }
 
 pub(crate) async fn initialize_client(client: &RmcpClient) -> anyhow::Result<()> {
+    initialize_client_with_timeout(client, Duration::from_secs(/*secs*/ 5)).await
+}
+
+pub(crate) async fn initialize_client_with_timeout(
+    client: &RmcpClient,
+    timeout: Duration,
+) -> anyhow::Result<()> {
     client
         .initialize(
             init_params(),
-            Some(Duration::from_secs(5)),
+            Some(timeout),
             Box::new(|_, _| {
                 async {
                     Ok(ElicitationResponse {