model version for Potential class is modified

[kenko911]

Summary

The model version of the Potential class is changed from 1 to 2. This prevents the wrong loading of the model.

Checklist

• [x] Google format doc strings added. Check with ruff.
• [x] Type annotations included. Check with mypy.
• [x] Tests added for new features/fixes.
• [x] If applicable, new classes/functions/modules have duecredit @due.dcite decorators to reference relevant papers by DOI (example)

Tip: Install pre-commit hooks to auto-check types and linting before every commit:

pip install -U pre-commit
pre-commit install

[janosh]

@kenko911 What do you need from me?

[kenko911]

Hi @janosh, thanks for reporting the error. I just changed the model version and I would like to know if it fixes the error you reported in #193😁?

[janosh]

@shyuep already fixed the error in v0.9.0.

[shyuep]

@janosh Yes it is fixed. But this is more for future-proofness. We want a proper versioning of model so that the cache invalidation works properly. It is not related to the tests in pymatgen/downstream codes.