Use inherited create_task/cancel_task in PipelineTask

PipelineTask owns its TaskManager but is itself a BaseObject, so it
inherits create_task/cancel_task. Replace the explicit
self._task_manager.create_task(coro, f"{self}::name") call sites with
self.create_task(coro, "name") for consistency with other BaseObject
subclasses.

src/pipecat/pipeline/task.py

@@ -1013,7 +1013,7 @@ class PipelineTask(BasePipelineTask):
 
     def _print_dangling_tasks(self):
         """Log any dangling tasks that haven't been properly cleaned up."""
-        tasks = [t.get_name() for t in self._task_manager.current_tasks()]
+        tasks = [t.get_name() for t in self.task_manager.current_tasks()]
         if tasks:
             logger.warning(f"{self} dangling tasks detected: {tasks}")