Implement YOLOv5 model with training pipeline - Add core YOLOv5 archi…

…tecture (Conv, Bottleneck, C3, SPPF, Detect) - Implement custom loss function (YOLOLoss) - Add utility functions (bbox_iou, non_max_suppression, xywh2xyxy) - Create basic training loop and data loading structure - Set up main function with argument parsing for easy execution