Reduce idle CPU from thread pools (#24652)

* reduce idle cpu from onnxruntime and opencv thread pools

ONNX Runtime's intra-op threads kept spinning for about 1 s after every run, so a CPU enrichment called once a second or more kept most cores busy. On a 16 thread machine, arcface at one call per second used 9.4 s of CPU per call with ~360 ms latency. Enrichment sessions on the CPU execution provider now set `session.intra_op.allow_spinning` to 0, which drops that to 1.9 s with no latency change. Detector sessions and GPU providers are unchanged, since disabling spinning doubled yolov9-t latency on CPU (12 to 23 ms).

The output and embeddings processes now run OpenCV single threaded, like the camera tracking process. A 4 camera birdseye redraw at 1080p drops from 13.7 to 4.0 ms of CPU, and the full frame conversion in the enrichment processors from 23 to 2.7 ms, each adding about 1 ms of wall time.

* test that only cpu enrichment sessions disable ort spinning

* patch out the neural engine in the spinning test

frigate/output/output.py

@@ -8,6 +8,7 @@ import threading
 from multiprocessing.synchronize import Event as MpEvent
 from wsgiref.simple_server import make_server
 
+import cv2
 from ws4py.server.wsgirefserver import (
     WebSocketWSGIHandler,
     WebSocketWSGIRequestHandler,
@@ -122,6 +123,10 @@ class OutputProcess(FrigateProcess):
     def run(self) -> None:
         self.pre_run_setup(self.config.logger)
 
+        # birdseye resizes are small, and OpenCV's per-core thread pool burns
+        # ~3x the CPU of running them inline
+        cv2.setNumThreads(1)
+
         frame_manager = SharedMemoryFrameManager()
 
         # start a websocket server on 8082