Fix import of ASE filters when user has installed from PyPI and not gitlab

[esoteric-ephemera]

Simple fix for a recent change to atomate2.forcefields.utils which tries to import FrechetCellFilter from ase.filters. Neither that filter nor the module in ASE exist in the current PyPI release.

I don't know that it's reasonable to expect users to install ASE from gitlab by default. I've added a kwarg to ase.filters.utils.Relaxer.relax that fails when FrechetCellFilter cannot be imported and the user does not specify and alternate Filter.

Added test coverage for atomate2.forcefields.utils to ensure higher Codecov

[codecov]

Codecov Report

Attention: 4 lines in your changes are missing coverage. Please review.

Comparison is base (2c23435) 76.05% compared to head (d691bd5) 75.95%.
Report is 6 commits behind head on main.

❗ Current head d691bd5 differs from pull request most recent head aea46e1. Consider uploading reports for the commit aea46e1 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #650      +/-   ##
==========================================
- Coverage   76.05%   75.95%   -0.10%     
==========================================
  Files          83       83              
  Lines        7033     7034       +1     
  Branches     1044     1044              
==========================================
- Hits         5349     5343       -6     
- Misses       1363     1373      +10     
+ Partials      321      318       -3     

Files	Coverage Δ
src/atomate2/forcefields/utils.py	83.56% <55.55%> (+5.78%)	⬆️

... and 1 file with indirect coverage changes

[esoteric-ephemera]

I think something is bugged with codecov here. Test coverage of the only file I've modified, atomate2.forcefields.utils, is at 82%. It's claiming that atomate2.common.jobs.utils has indirect test coverage decrease of -33%, which makes no sense given that these two files are unrelated.