moved v8 nms to dedicated function for better readibility, adapted v8…

… nms logic to match code used in https://github.com/ultralytics/ultralytics.git/examples/YOLOv8-ONNXRuntime/main.py

nms.py

@@ -55,6 +55,9 @@ def non_max_suppresion_v8(prediction, conf_thres=0.25, iou_thres=0.45, classes=N
                         labels=(), max_det=300):
     # TODO: Test this for changed parameter number in yolov8!!! All that could be detected with last commit were persons!
 
+    nc = prediction.shape[2] - 5  # number of classes
+    xc = prediction[..., 4] > conf_thres  # candidates
+
     # Checks
     assert 0 <= conf_thres <= 1, f'Invalid Confidence threshold {conf_thres}, valid values are between 0.0 and 1.0'
     assert 0 <= iou_thres <= 1, f'Invalid IoU {iou_thres}, valid values are between 0.0 and 1.0'