Add broadcast_interruption() to FrameProcessor

Replace the round-trip push_interruption_task_frame_and_wait() mechanism
with broadcast_interruption(), which pushes an InterruptionFrame both
upstream and downstream directly from the calling processor.

This eliminates race conditions (transcription arriving before the
InterruptionFrame comes back), swallowed-event timeouts (frame blocked
before reaching the sink), and the complexity of _wait_for_interruption
flag / queue bypass / frame.complete() obligations.

- Add broadcast_interruption() to FrameProcessor
- Deprecate push_interruption_task_frame_and_wait() (delegates to new method)
- Remove event field and complete() from InterruptionFrame/InterruptionTaskFrame
- Remove _wait_for_interruption flag and all special-case logic
- Remove frame.complete() calls in stt_mute_filter and llm_response_universal
- Update all 17 call sites to use broadcast_interruption()
- Update tests

tests/test_context_aggregators.py

@@ -21,7 +21,6 @@ from pipecat.frames.frames import (
     FunctionCallResultProperties,
     InterimTranscriptionFrame,
     InterruptionFrame,
-    InterruptionTaskFrame,
     LLMContextAssistantTimestampFrame,
     LLMContextFrame,
     LLMFullResponseEndFrame,
@@ -567,7 +566,7 @@ class BaseTestUserContextAggregator:
             SleepFrame(),
             UserStoppedSpeakingFrame(),
         ]
-        expected_up_frames = [InterruptionTaskFrame]
+        expected_up_frames = [InterruptionFrame]
         expected_down_frames = [
             BotStartedSpeakingFrame,
             UserStartedSpeakingFrame,