Make it so that AIService is the exclusive "syncer" of model name to metrics.

The only (rare) exception—where a service directly still needs to directly call `self._sync_model_name_to_metrics()`—is when the model name need to be "pulled" from another field (or nested field) in settings up to settings.model on a settings update. This only occurs in Deepgram services, where we use the voice as the model name.

This change has the side-effect of bringing model name to metrics for a number of services that were accidentally omitting it before.

src/pipecat/services/fal/image.py

@@ -13,6 +13,7 @@ for creating images from text prompts using various AI models.
 import asyncio
 import io
 import os
+from dataclasses import dataclass
 from typing import AsyncGenerator, Dict, Optional, Union
 
 import aiohttp
@@ -22,6 +23,7 @@ from pydantic import BaseModel
 
 from pipecat.frames.frames import ErrorFrame, Frame, URLImageRawFrame
 from pipecat.services.image_service import ImageGenService
+from pipecat.services.settings import ImageGenSettings
 
 try:
     import fal_client
@@ -31,6 +33,15 @@ except ModuleNotFoundError as e:
     raise Exception(f"Missing module: {e}")
 
 
+@dataclass
+class FalImageGenSettings(ImageGenSettings):
+    """Settings for the Fal image generation service.
+
+    Parameters:
+        model: Fal.ai model identifier.
+    """
+
+
 class FalImageGenService(ImageGenService):
     """Fal's image generation service.
 
@@ -77,9 +88,7 @@ class FalImageGenService(ImageGenService):
             key: Optional API key for Fal.ai. If provided, sets FAL_KEY environment variable.
             **kwargs: Additional arguments passed to parent ImageGenService.
         """
-        super().__init__(**kwargs)
-        self._settings.model = model
-        self._sync_model_name_to_metrics()
+        super().__init__(settings=FalImageGenSettings(model=model), **kwargs)
         self._params = params
         self._aiohttp_session = aiohttp_session
         if key: