Add missing step 3 comment to LLM service init methods

Adds the explicit "no params object" step 3 comment to all
LLM services that skip from step 2 to step 4 in their
settings initialization sequence, matching the pattern
established in services that do have a params object.

src/pipecat/services/cerebras/llm.py

@@ -64,6 +64,8 @@ class CerebrasLLMService(OpenAILLMService):
             _warn_deprecated_param("model", CerebrasLLMSettings, "model")
             default_settings.model = model
 
+        # 3. (No step 3, as there's no params object to apply)
+
         # 4. Apply settings delta (canonical API, always wins)
         if settings is not None:
             default_settings.apply_update(settings)