Custom classes for Process and Metrics (#13950)

* Subclass Process for audio_process

* Introduce custom mp.Process subclass

In preparation to switch the multiprocessing startup method away from
"fork", we cannot rely on os.fork cloning the log state at fork time.
Instead, we have to set up logging before we run the business logic of
each process.

* Make camera_metrics into a class

* Make ptz_metrics into a class

* Fixed PtzMotionEstimator.ptz_metrics type annotation

* Removed pointless variables

* Do not start audio processor when no audio cameras are configured

frigate/object_detection.py

@@ -10,6 +10,7 @@ from abc import ABC, abstractmethod
 import numpy as np
 from setproctitle import setproctitle
 
+import frigate.util as util
 from frigate.detectors import create_detector
 from frigate.detectors.detector_config import InputTensorEnum
 from frigate.util.builtin import EventsPerSecond, load_labels
@@ -168,7 +169,7 @@ class ObjectDetectProcess:
         self.detection_start.value = 0.0
         if (self.detect_process is not None) and self.detect_process.is_alive():
             self.stop()
-        self.detect_process = mp.Process(
+        self.detect_process = util.Process(
             target=run_detector,
             name=f"detector:{self.name}",
             args=(