Implement utilities for V-COCO

Looking forward to adding support for vcoco evaluation.

Lines 96 to 99 in 1927430

    
           if args.eval: 
        
               if args.dataset == 'vcoco': 
        
                   raise NotImplementedError(f"Evaluation on V-COCO has not been implemented.") 
        
               ap = engine.test_hico(test_loader)

Hi, @fredzzhang .
I found cache.pkl to eval vcoco is too slow, it need spend 30mins( I think it is the v-coco repository code problem ).
Do you have any suggestions to speed up it?

	if args.eval:
	if args.dataset == 'vcoco':
	raise NotImplementedError(f"Evaluation on V-COCO has not been implemented.")
	ap = engine.test_hico(test_loader)