Reference issues: #5157 , #343 , #7011

The current version of the export.py script outputs a CoreML model without NMS. This means that certain Vision APIs cannot be used with the model directly, as the output during inference is VNCoreMLFeatureValueObservation. The changes implemented here add a NMS layer to the CoreML output, so the output from inference is VNRecognizedObjectObservation. By adding NMS to the model directly, as opposed to later in code, the performance of the overall image/video processing is improved. This also allows use of the "Preview" tab in Xcode for quickly testing the model.

Default IoU and confidence thresholds are taken from the `--iou-thres` and `--conf-thres` arguments during export.py script runtime. The user can also change these later by using a CoreML MLFeatureProvider in their application (see [https://developer.apple.com/documentation/coreml/mlfeatureprovider](https://developer.apple.com/documentation/coreml/mlfeatureprovider)).

This has no effect on training, as it only adds an additional layer during CoreML export for NMS.

for more information, see https://pre-commit.ci

for more information, see https://pre-commit.ci