Awesome!

Very happy to see this ported to Metal. Now that I've given up on S4TF, it would be interesting to learn of a Swift framework (s4nnc) that runs deep learning on Metal. Regardless, I'll probably use MPSGraph directly in my future work instead of a high-level API. I haven't seen the `nnc` directory of this repo get changes, but will that be ported to Metal soon? I also haven't seen Metal shader files yet, while there are custom CUDA shaders. Don't be afraid to use MSL for operations not supported by MPSGraph. <img width="337" alt="Screenshot 2022-11-25 at 10 41 27 PM" src="https://user-images.githubusercontent.com/71743241/204071178-bc693cd4-34a0-4354-8734-a1b76462fff6.png">