Support prediction of list of sources, in-memory dataset and other improvements (#685)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

ultralytics/yolo/v8/detect/predict.py

@@ -42,7 +42,7 @@ class DetectionPredictor(BasePredictor):
             im = im[None]  # expand for batch dim
         self.seen += 1
         im0 = im0.copy()
-        if self.webcam or self.from_img:  # batch_size >= 1
+        if self.source_type.webcam or self.source_type.from_img:  # batch_size >= 1
             log_string += f'{idx}: '
             frame = self.dataset.count
         else: