improve task creation and cancellation

If a FrameProcessor needs to create a task it should use
FrameProcessor.create_task() and FrameProcessor.cancel_task(). This gives
Pipecat more control over all the tasks that are created in Pipecat.

Both functions internally use the utils module: utils.create_task() and
utils.cancel_task() which should also be used outside of FrameProcessors. That
is, unless strictly necessary, we should avoid using asyncio.create_task().

src/pipecat/services/lmnt.py

@@ -113,16 +113,13 @@ class LmntTTSService(TTSService, WebsocketService):
     async def _connect(self):
         await self._connect_websocket()
 
-        self._receive_task = self.get_event_loop().create_task(
-            self._receive_task_handler(self.push_error)
-        )
+        self._receive_task = self.create_task(self._receive_task_handler(self.push_error))
 
     async def _disconnect(self):
         await self._disconnect_websocket()
 
         if self._receive_task:
-            self._receive_task.cancel()
-            await self._receive_task
+            await self.cancel_task(self._receive_task)
             self._receive_task = None
 
     async def _connect_websocket(self):