Cleanup on aisle METRICS. Note: See below, this is a breaking change

1. Fleshed out MetricsFrames and broke it into a proper set of types
2. Add model_name as a property to the AIService so that it can be
   automatically included in metrics and also remove that
   overhead from all the various services themselves

Breaking change!

Because of the types improvements, the MetricsFrame type has
changed. Each frame will have a list of metrics simlilar to before
except each item in the list will only contain one type of metric:
"ttfb", "tokens", "characters", or "processing". Previously these
fields would be in every entry but set to None if they didn't apply.

While this changes internal handling of the MetricsFrame, it does NOT
break the RTVI/daily messaging of metrics. That format remains the same.

Also. Remember to use model_name for accessing a service's current
model and set_model_name for setting it.

src/pipecat/services/ai_services.py

@@ -32,6 +32,7 @@ from pipecat.frames.frames import (
     UserImageRequestFrame,
     VisionImageRawFrame
 )
+from pipecat.metrics.metrics import MetricsData
 from pipecat.processors.frame_processor import FrameDirection, FrameProcessor
 from pipecat.transcriptions.language import Language
 from pipecat.utils.audio import calculate_audio_volume
@@ -46,6 +47,15 @@ from loguru import logger
 class AIService(FrameProcessor):
     def __init__(self, **kwargs):
         super().__init__(**kwargs)
+        self._model_name: str = ""
+
+    @property
+    def model_name(self) -> str:
+        return self._model_name
+
+    def set_model_name(self, model: str):
+        self._model_name = model
+        self.set_core_metrics_data(MetricsData(processor=self.name, model=self._model_name))
 
     async def start(self, frame: StartFrame):
         pass
@@ -158,7 +168,7 @@ class TTSService(AIService):
 
     @abstractmethod
     async def set_model(self, model: str):
-        pass
+        self.set_model_name(model)
 
     @abstractmethod
     async def set_voice(self, voice: str):
@@ -367,7 +377,7 @@ class STTService(AIService):
 
     @abstractmethod
     async def set_model(self, model: str):
-        pass
+        self.set_model_name(model)
 
     @abstractmethod
     async def set_language(self, language: Language):