fix(MVLSlabSet): convert DIPOL vector to pure Python list before writing INCAR

[atulcthakur]

Summary

When auto_dipole=True, MVLSlabSet was passing a NumPy array into the INCAR’s DIPOL tag, causing pymatgen to serialize it with brackets (e.g. DIPOL = [0.1 0.2 0.3]). VASP expects three space‑separated floats without any brackets: https://www.vasp.at/wiki/index.php/DIPOL.
This PR converts the computed center‑of‑mass array into a plain Python list[float] (via .tolist()), ensuring the INCAR writes
DIPOL = 0.1 0.2 0.3
instead of
DIPOL = [0.1 0.2 0.3]
which errors out with the recent VASP 6.4.

Major changes:

• fix 1: In MVLSlabSet.incar_updates, replace center_of_mass (a NumPy array) with a pure python list = com.tolist()

Checklist

• Google format doc strings added. Check with ruff.
• Type annotations included. Check with mypy.
• Tests added for new features/fixes.
• 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

[shyuep]

Add a unit test pls.