Add Apple Silicon (MPS) support

[provos]

Adds MPS device support for both image and video predictors on Apple Silicon.

Changes:

• Add get_default_device() utility that detects MPS availability
• Fix device mismatches (coords cache, freqs_cis cache)
• Add MPS workaround for complex tensor repeat() in RoPE
• Make torch._assert_async conditional on CUDA
• Fix MPS memory leak in video predictor via synchronization points

Performance of the Video predictor:

• ~3x faster than CPU
• Runs with ~38GB peak memory. This is due to the way that MPS caches graphs. Before adding the synchronization points, running the video predictor would consume all available memory.

[mattiagaggi]

this seems to overlap with your other pull request :)

Also I'd make some tests

[provos]

This is a continuation of the other PR. I just didn't want to clutter things when I didn't know yet how hard MPS support was going to be. I can add the end-to-end test for the video predictor to the PR but didn't want to pollute your repo. Is there a place you would like tests to go?

[drduhe]

This looks awesmoe and does a better job that was I was getting at in my PR, #326 in addressing the Mac deployments. I am going to remove that logic from my PR now seeing that this is in the pipeline.

[provos]

@drduhe do you know why the import is stuck? i noticed the same with my other PR which was approved a week(?) ago?

[drduhe]

@drduhe do you know why the import is stuck? i noticed the same with my other PR which was approved a week(?) ago?

@provos I am not a maintainer on the project so it probably needs to get approval from someone with more pull than I have =). But FWIW I did create a tests directory as part of my PR as a starting point for where we can put unit tests. @mattiagaggi might have more information on the process, SLA, and workflow requirements.

[nico1996it]

It would be great to have this merged...