Support for electrostatics

[orionarcher]

Summary

• Add charge and spin to SimState
• Add charge and spin support for MaceModel
• Add charge and spin support for FairchemModel

Checklist

Before a pull request can be merged, the following items must be checked:

• Doc strings have been added in the Google docstring format.
• Run ruff on your code.
• Tests have been added for any new functionality or bug fixes.

[thomasloux]

Look good to me.
Are we sure that the standard value for all of these models is spin=0 charge=0. It would make sense but I'm not sure it's case when I looked at it, but I'm not sure.

[curtischong]

I think this looks fine

[orionarcher]

Are we sure that the standard value for all of these models is spin=0 charge=0. It would make sense but I'm not sure it's case when I looked at it, but I'm not sure.

Good question. I am not sure, but it seems like a better default to me than torch.nan. If someone is using one of the models, I think it's reasonable to ask them to attend to setting the charge and spin.