Fix stale state in user turn stop strategies between turns

Reset stop strategies at turn start (not just turn stop) so that late
transcriptions arriving between turns do not leave stale _text that
causes premature stops on the next turn. Also cancel pending timeout
tasks in reset() for both SpeechTimeout and TurnAnalyzer strategies.

src/pipecat/turns/user_stop/speech_timeout_user_turn_stop_strategy.py

@@ -64,6 +64,9 @@ class SpeechTimeoutUserTurnStopStrategy(BaseUserTurnStopStrategy):
         self._vad_user_speaking = False
         self._transcript_finalized = False
         self._vad_stopped_time = None
+        if self._timeout_task:
+            await self.task_manager.cancel_task(self._timeout_task)
+            self._timeout_task = None
 
     async def setup(self, task_manager: BaseTaskManager):
         """Initialize the strategy with the given task manager.

src/pipecat/turns/user_stop/turn_analyzer_user_turn_stop_strategy.py

@@ -68,6 +68,9 @@ class TurnAnalyzerUserTurnStopStrategy(BaseUserTurnStopStrategy):
         self._vad_user_speaking = False
         self._vad_stopped_time = None
         self._transcript_finalized = False
+        if self._timeout_task:
+            await self.task_manager.cancel_task(self._timeout_task)
+            self._timeout_task = None
 
     async def setup(self, task_manager: BaseTaskManager):
         """Initialize the strategy with the given task manager.

src/pipecat/turns/user_turn_controller.py

@@ -256,6 +256,10 @@ class UserTurnController(BaseObject):
         for s in self._user_turn_strategies.start or []:
             await s.reset()
 
+        # Reset all user turn stop strategies to start fresh for the new turn.
+        for s in self._user_turn_strategies.stop or []:
+            await s.reset()
+
         await self._call_event_handler("on_user_turn_started", strategy, params)
 
     async def _trigger_user_turn_stop(