refactor imports to use dino namespace

dino/eval_copy_detection.py

dino/eval_image_retrieval.py

dino/eval_knn.py

dino/eval_linear.py

dino/eval_video_segmentation.py

dino/main_dino.py

dino/run_with_submitit.py

dino/video_generation.py

dino/vision_transformer.py

dino/visualize_attention.py