using GufeQuantity instead of deprecated OpenFF models

[ijpulidos]

These changes align with the new changes upstream in gufe where the gufe.vendor.openff.models module has been removed in favor of using the GufeQuantity as specified in the docs https://gufe.openfree.energy/en/latest/how-tos/custom_quantities.html

This now also makes us depend on gufe >=1.7.0 for the CI environment.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.35%. Comparing base (639b258) to head (73b6bb1).
⚠️ Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #130      +/-   ##
==========================================
- Coverage   86.86%   86.35%   -0.51%     
==========================================
  Files          11       11              
  Lines        1439     1444       +5     
==========================================
- Hits         1250     1247       -3     
- Misses        189      197       +8     

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[ijpulidos]

To be fair, this kinda opened up other issues we had. Such as keeping up with the new default options/behavior upstream (for example the platform change). I wonder if we should rename this PR to reflect those changes.

[atravitz]

LGTM - thanks for being flexible with this pydantic migration @ijpulidos!

Just one note that you might want to minimum pin gufe to 1.7.1, up to you though.