Feature python train.py --cache disk (#4049)

* Add cache-on-disk and cache-directory to cache images on disk

* Fix load_image with cache_on_disk

* Add no_cache flag for load_image

* Revert the parts('logging' and a new line) that do not need to be modified

* Add the assertion for shapes of cached images

* Add a suffix string for cached images

* Fix boundary-error of letterbox for load_mosaic

* Add prefix as cache-key of cache-on-disk

* Update cache-function on disk

* Add psutil in requirements.txt

* Update train.py

* Cleanup1

* Cleanup2

* Skip existing npy

* Include re-space

* Export return character fix

Co-authored-by: Glenn Jocher <glenn.jocher@ultralytics.com>

export.py

@@ -156,8 +156,8 @@ def run(weights='./yolov5s.pt',  # weights path
 
     # Finish
     print(f'\nExport complete ({time.time() - t:.2f}s)'
-          f"Results saved to {colorstr('bold', file.parent.resolve())}\n"
-          f'Visualize with https://netron.app')
+          f"\nResults saved to {colorstr('bold', file.parent.resolve())}"
+          f'\nVisualize with https://netron.app')
 
 
 def parse_opt():