Mark abstract image/vision generators as real async generators

`ImageGenService.run_image_gen` and `VisionService.run_vision` were
declared `async def ... -> AsyncGenerator[Frame, None]` with `pass`
bodies. Without a `yield` anywhere in the body, Python treats the
function as a coroutine returning an `AsyncGenerator`, not as an async
generator itself, so callers got a coroutine where they expected an
iterator.

Add `raise NotImplementedError; yield` so the body contains a yield
(making this a real async generator) while still raising cleanly if a
subclass ever calls `super().run_*` by mistake.

pyrightconfig.json

@@ -76,7 +76,6 @@
     "src/pipecat/services/heygen/client.py",
     "src/pipecat/services/heygen/video.py",
     "src/pipecat/services/hume/tts.py",
-    "src/pipecat/services/image_service.py",
     "src/pipecat/services/inworld/realtime/llm.py",
     "src/pipecat/services/inworld/tts.py",
     "src/pipecat/services/kokoro/tts.py",
@@ -115,7 +114,6 @@
     "src/pipecat/services/tavus/video.py",
     "src/pipecat/services/tts_service.py",
     "src/pipecat/services/ultravox/llm.py",
-    "src/pipecat/services/vision_service.py",
     "src/pipecat/services/websocket_service.py",
     "src/pipecat/services/whisper/stt.py",
     "src/pipecat/services/xai/realtime/events.py",