Describe the bug
While working on Streaming I relaized we have a few inconsistencies in our HuggingFaceLocalChatGenerator component with regards to the streaming callback.

• We define the type of the streaming_callback in the run_async function incorrectly to be a sync signature

  haystack/haystack/components/generators/chat/hugging_face_local.py

  Line 495 in 9ae76e1

  streaming_callback: Optional[Callable[[StreamingChunk], None]] = None,

• and here

  haystack/haystack/components/generators/chat/hugging_face_local.py

  Line 549 in 9ae76e1

  streaming_callback: Callable[[StreamingChunk], None],

• We require it to be an async method here

  haystack/haystack/components/generators/chat/hugging_face_local.py

  Line 534 in 9ae76e1

  streaming_callback = select_streaming_callback(self.streaming_callback, streaming_callback, requires_async=True)

• And we use HFTokenStreamingHandler which is a sync only streaming handler. So we actually need to create an async version of this for streaming to work properly with run_async. Line in question is here

  haystack/haystack/components/generators/chat/hugging_face_local.py

  Line 569 in 9ae76e1

  generation_kwargs["streamer"] = HFTokenStreamingHandler(tokenizer, streaming_callback, stop_words)

Expected behavior
Use a async version of HFTokenStreamingHandler and update the type signature

To Reproduce
If you update the types to be the AsyncStreamCallbackT mypy will throw an error saying HFTokenStreamingHandler is not compatible