feat: Support MacOS MPS/CPU

[Tohrusky]

https://github.com/EmbarkStudios/pdm-plugin-torch/blob/main/pdm-plugin-torch/pdm_plugin_torch/config.py#L43C30-L43C30

There is no way to download the wheel package for MacOS currently, or we can just download it directly from pypi?

[tgolsson]

Hey!

I'd love a better solution. Before the recent release; we'd actually not use a tag at all for CPU. But that lead to bad behavior in other cases, where we'd end up with GPU-compatible binaries from pypi when it failed to find a suitable CPU variant. So I opted for being more literal, but now Mac is broken (again).

A PR to improve this would be very welcome. I'm wondering whether one could simply use markers to say ...+cpu; os != darwin and ...; os = darwin -- in the CPU case.