Update MOF-303 mace model.

[hdsassnick]

Pull Request

Description 📝

This PR merely updates the MOF-303 mace MLIP to match the one used in the FLAMES paper.

Changes Proposed 🔧

• This only affects the tests for the GCMC, TMMC, Widom classes.

Related Issues 📎

Before submitting 📌

• I've read and followed all steps in the Making a pull request
  section of the CONTRIBUTING docs.
• I've updated or added any relevant docstrings following the syntax described in the
  Writing docstrings section of the CONTRIBUTING docs.
• If this PR fixes a bug, I've added a test that will fail without my fix.
• If this PR adds a new feature, I've added tests that sufficiently cover my new functionality.

Testing Instructions 🧪

Additional Notes 💬