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/lmnt/tts.py

@@ -92,6 +92,8 @@ class LmntTTSService(InterruptibleTTSService):
     language settings.
     """
 
+    _settings: LmntTTSSettings
+
     def __init__(
         self,
         *,
@@ -122,7 +124,7 @@ class LmntTTSService(InterruptibleTTSService):
         self._api_key = api_key
         self._voice_id = voice_id
         self.set_model_name(model)
-        self._settings: LmntTTSSettings = LmntTTSSettings(
+        self._settings = LmntTTSSettings(
             model=model,
             voice=voice_id,
             language=self.language_to_service_language(language),