add support to macOS GPU for inference

[huiofficial]

Use torch.backends.mps.is_available() to check whether GPU is available for PyTorch on macOS.

Use to.(xx.device) to match op device for computing.

Use os.environ['PYTORCH_ENABLE_MPS_FALLBACK'] = '1' to deal with operator 'aten::grid_sampler_3d' is not currently implemented for the MPS device.

And I optimized imports in inference.py

[yukiarimo]

How fast is it?

[bruno-cunha]

How fast is it?

I tested it in my M1 and got 2x faster

[huiofficial]

thanks, it'd be better if u can give a review.