enable tuning or auto-tuning of framerate for processing on slower devices

[cdiddy77]

On android, even though we are running the mediapipe processor asynchronously, we are currently forced to convert the image from yuv to rgb as part of every frame, which makes it impossible to maintain 30fps especially on slower devices

https://react-native-vision-camera.com/docs/guides/frame-processors#running-at-a-throttled-fps-rate documents a mechanism that visioncamera provides for doing frame processing more seldom than the full frame rate of the camera.

Experiment with using the inference time to auto-tune the target fps. If that doesn't work, then at least provide a reasonable default setting on android and allow the client to override the target fps.