Add torch neuron support for scvi tools

[LinearParadox]

Torch neuron is a PyTorch architecture that enables it to use AWS based Trainium and Inferentia gpu instances. Since these are somewhat cheaper, especially for large models that may be a little too large for GPUs such as T4s, but also not worth an A100. It would be a nice addition

[martinkim0]

I'm not familiar with torch-neuron, what sort of changes would be necessary in order to enable this?

[LinearParadox]

I think there would likely have to be some analogous code added. For example something like:

if use_neuron:
    Neuron training code
else:
    normal training code

The API seems pretty analogous to PyTorch:

https://awsdocs-neuron.readthedocs-hosted.com/en/latest/frameworks/torch/torch-neuronx/programming-guide/training/pytorch-neuron-programming-guide.html#pytorch-neuronx-programming-guide

I'm not super experienced with torch, but I can also try to dig in after this week to try and see if it's a trivial modification or entails a larger redesign.

The one major difference that might pose an issue is that neuron builds graphs lazily, while PyTorch doesn't. Not sure how impactful this will be practically though

[martinkim0]

Let me know if you're able to look into this! Would be happy to take a PR if it's a small modification. If it seems like it's going to be a larger redesign, I think it would make sense for us to discuss it internally before anything is implemented.