all frame processors are asynchrnous

In this commit we make all frame processors asynchronous, that is, they have an
internal queue and they push frames using a task from that queue.

examples/foundational/05-sync-speech-and-image.py

@@ -86,13 +86,13 @@ async def main():
             ),
         )
 
+        llm = OpenAILLMService(api_key=os.getenv("OPENAI_API_KEY"), model="gpt-4o")
+
         tts = CartesiaHttpTTSService(
             api_key=os.getenv("CARTESIA_API_KEY"),
             voice_id="79a125e8-cd45-4c13-8a67-188112f4dd22",  # British Lady
         )
 
-        llm = OpenAILLMService(api_key=os.getenv("OPENAI_API_KEY"), model="gpt-4o")
-
         imagegen = FalImageGenService(
             params=FalImageGenService.InputParams(image_size="square_hd"),
             aiohttp_session=session,
@@ -107,8 +107,10 @@ async def main():
         # that, each pipeline runs concurrently and `SyncParallelPipeline` will
         # wait for the input frame to be processed.
         #
-        # Note that `SyncParallelPipeline` requires all processors in it to be
-        # synchronous (which is the default for most processors).
+        # Note that `SyncParallelPipeline` requires the last processor in each
+        # of the pipelines to be synchronous. In this case, we use
+        # `CartesiaHttpTTSService` and `FalImageGenService` which make HTTP
+        # requests and wait for the response.
         pipeline = Pipeline(
             [
                 llm,  # LLM

examples/foundational/05a-local-sync-speech-and-image.py

@@ -82,6 +82,7 @@ async def main():
                         self.frame = OutputAudioRawFrame(
                             bytes(self.audio), frame.sample_rate, frame.num_channels
                         )
+                    await self.push_frame(frame, direction)
 
             class ImageGrabber(FrameProcessor):
                 def __init__(self):
@@ -93,6 +94,7 @@ async def main():
 
                     if isinstance(frame, URLImageRawFrame):
                         self.frame = frame
+                    await self.push_frame(frame, direction)
 
             llm = OpenAILLMService(api_key=os.getenv("OPENAI_API_KEY"), model="gpt-4o")
 
@@ -121,8 +123,10 @@ async def main():
             # `SyncParallelPipeline` will wait for the input frame to be
             # processed.
             #
-            # Note that `SyncParallelPipeline` requires all processors in it to
-            # be synchronous (which is the default for most processors).
+            # Note that `SyncParallelPipeline` requires the last processor in
+            # each of the pipelines to be synchronous. In this case, we use
+            # `CartesiaHttpTTSService` and `FalImageGenService` which make HTTP
+            # requests and wait for the response.
             pipeline = Pipeline(
                 [
                     llm,  # LLM