Add mutually exclusive pytorch backend extras

[Kaweees]

Summary

This pull request adds selectable PyTorch backends. This extends LuckyLab to devices which support Apple Metal or CUDA 13.

Changes

• Add selectable PyTorch backends so LuckyLab supports CPU/Apple Metal and multiple CUDA versions without forcing an incompatible wheel index.

Related Issues

Fixes #(issue number)

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring (no functional changes)

Testing

• I have added tests that prove my fix is effective or that my feature works
• New and existing tests pass locally with my changes

Checklist

• My code follows the project's code style
• I have performed a self-review of my code
• I have commented my code where necessary
• I have updated the documentation if needed
• My changes generate no new warnings

[Kaweees]

The only thing missing is updating the following README lines. Got caught up in decision paralysis when modifying it, any ideas?