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/cerebras/llm.py

@@ -66,7 +66,7 @@ class CerebrasLLMService(OpenAILLMService):
             Dictionary of parameters for the chat completion request.
         """
         params = {
-            "model": self.model_name,
+            "model": self._settings.model,
             "stream": True,
             "seed": self._settings.seed,
             "temperature": self._settings.temperature,