Fix asyncio.Event race conditions in idle processors

Move event.clear() from finally block to success path in
IdleFrameProcessor and UserIdleProcessor._idle_task_handler().
The finally block unconditionally cleared signals set during
async timeout callbacks, causing false-positive idle detection.

Closes #3402

src/pipecat/processors/idle_frame_processor.py

@@ -85,7 +85,6 @@ class IdleFrameProcessor(FrameProcessor):
         while True:
             try:
                 await asyncio.wait_for(self._idle_event.wait(), timeout=self._timeout)
+                self._idle_event.clear()
             except asyncio.TimeoutError:
                 await self._callback(self)
-            finally:
-                self._idle_event.clear()