Update AIService.set_model_name to AIService._sync_model_name_to_metrics to:

- indicate clearly that it's not meant for public use
- make it clear the `self._settings` is the single source of truth for model information
- set the stage for an upcoming change where `AIService` subclasses won't have to ever worry about explicitly calling an `AIService` method to sync model name to metrics

Across all services, switch from accessing `self._model_name` or `self.model_name` in favor of `self._settings.model`.

src/pipecat/services/lmnt/tts.py

@@ -122,13 +122,13 @@ class LmntTTSService(InterruptibleTTSService):
         )
 
         self._api_key = api_key
-        self.set_model_name(model)
         self._settings = LmntTTSSettings(
             model=model,
             voice=voice_id,
             language=self.language_to_service_language(language),
             format="raw",
         )
+        self._sync_model_name_to_metrics()
         self._receive_task = None
         self._context_id: Optional[str] = None
 
@@ -238,7 +238,7 @@ class LmntTTSService(InterruptibleTTSService):
                 "format": self._settings.format,
                 "sample_rate": self.sample_rate,
                 "language": self._settings.language,
-                "model": self.model_name,
+                "model": self._settings.model,
             }
 
             # Connect to LMNT's websocket directly