Refactor to only depend on pymatgen-core

[kavanase]

Minor refactor so that pyrho only requires pymatgen-core and not the full pymatgen package.

Contributor Checklist

• I have run the tests locally and they passed.
  - [ ] I have added tests, or extended existing tests, to cover any new features or bugs fixed in this PR

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.93%. Comparing base (b82e926) to head (3aaf01d).
⚠️ Report is 56 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #133      +/-   ##
==========================================
+ Coverage   79.27%   79.93%   +0.66%     
==========================================
  Files           5        5              
  Lines         304      324      +20     
==========================================
+ Hits          241      259      +18     
- Misses         63       65       +2     

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[kavanase]

The only failure here is the docs deployment with:

Error: Action failed with "not found deploy key or tokens"

I assume because docs building only works when run on the main branch?

[jmmshn]

@kavanase thanks!
I will fix the docs wf