Add class-level _settings type annotations to all service classes for better editor support.

Standardize all STT, TTS, and LLM service classes to declare `_settings` with the narrowed Settings type as a class-level annotation. This gives editors and type checkers the specific type when hovering or autocompleting on `self._settings` in each service and its subclasses. Inline `self._settings: Type = ...` assignments are replaced with plain `self._settings = ...`.

src/pipecat/services/openai/stt.py

@@ -169,6 +169,8 @@ class OpenAIRealtimeSTTService(WebsocketSTTService):
         )
     """
 
+    _settings: OpenAIRealtimeSTTSettings
+
     def __init__(
         self,
         *,
@@ -231,7 +233,7 @@ class OpenAIRealtimeSTTService(WebsocketSTTService):
         self._noise_reduction = noise_reduction
         self._should_interrupt = should_interrupt
 
-        self._settings: OpenAIRealtimeSTTSettings = OpenAIRealtimeSTTSettings(
+        self._settings = OpenAIRealtimeSTTSettings(
             model=model,
             language=language,
             prompt=prompt,