Fix #9169 refine idle timeout and failure

Only fail request callback if a failure has not been otherwise notified.
Slight optimization for failing idle timeouts by avoiding double lock.
Always create a failure if failing the callback.

jetty-core/jetty-server/src/main/java/org/eclipse/jetty/server/internal/HttpChannelState.java

@@ -387,7 +387,7 @@ public Runnable onIdleTimeout(TimeoutException t)
                     {
                         if (onIdleTimeout.test(t))
                         {
-                            // If the idle timeout listener(s) return true, then we call onFailure and any task it returns.
+                            // If the idle timeout listener(s) return true, then we call onFailure and run any task it returns.
                             Runnable task = onFailure(t);
                             if (task != null)
                                 task.run();