Fix duplicate model_paths kwarg

[ElliottKasoar]

Resolves issue with duplicated kwargs for mace_off and mace_mp.

The new tests throws an error without the fix, e.g.:

E       TypeError: mace.calculators.mace.MACECalculator() got multiple values for keyword argument 'model_paths'

../venv_janus_11_new/lib/python3.11/site-packages/mace/calculators/foundations_models.py:105: TypeError
------------------------------------------------------- Captured stdout call --------------------------------------------------------
Using Materials Project MACE for MACECalculator with /home/ek/.cache/mace/46jrkm3v
Using float64 for MACECalculator, which is slower but more accurate. Recommended for geometry optimization.
====================================================== short test summary info ======================================================
FAILED tests/test_mlip_calculators.py::test_mace[mace_mp-cpu-kwargs3] - TypeError: mace.calculators.mace.MACECalculator() got multiple values for keyword argument 'model_paths'