test(gateway): cover with_list_timeout (ok / err / timeout paths)

Adds unit tests for the feature-discovery list-call timeout helper introduced
in this PR: a completing future yields Some(Ok), an erroring future yields
Some(Err), and a never-resolving future yields None (timeout). The timeout
case runs under tokio's paused clock so it resolves instantly instead of
waiting the full 10s LIST_TIMEOUT.

Signed-off-by: Mohammod Al Amin Ashik <maa.ashik00@gmail.com>

Author: its-mash

crates/mcpmux-gateway/src/pool/features/discovery.rs

@@ -163,3 +163,36 @@ impl FeatureDiscoveryService {
             .await
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::future::pending;
+
+    #[tokio::test]
+    async fn with_list_timeout_returns_some_ok_when_future_completes() {
+        let out =
+            FeatureDiscoveryService::with_list_timeout("tools/list", async { Ok::<i32, &str>(42) })
+                .await;
+        assert!(matches!(out, Some(Ok(42))));
+    }
+
+    #[tokio::test]
+    async fn with_list_timeout_propagates_inner_error() {
+        let out = FeatureDiscoveryService::with_list_timeout("prompts/list", async {
+            Err::<i32, &str>("boom")
+        })
+        .await;
+        assert!(matches!(out, Some(Err("boom"))));
+    }
+
+    #[tokio::test(start_paused = true)]
+    async fn with_list_timeout_returns_none_on_timeout() {
+        // A future that never resolves. Under tokio's paused clock the runtime
+        // auto-advances to the LIST_TIMEOUT deadline, so this resolves to a
+        // timeout without actually waiting 10 seconds.
+        let never = pending::<Result<i32, &str>>();
+        let out = FeatureDiscoveryService::with_list_timeout("resources/list", never).await;
+        assert!(out.is_none());
+    }
+}