ChemEnv only when oxidation states exist

[JaGeo]

As mentioned in #595, this implementation reduces the run times by more than 50% and should therefore hopefully allow to integate the ChemEnv data

[codecov-commenter]

Codecov Report

Base: 92.74% // Head: 92.73% // Decreases project coverage by -0.00% ⚠️

Coverage data is based on head (831d439) compared to base (7e7fb98).
Patch coverage: 92.30% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #596      +/-   ##
==========================================
- Coverage   92.74%   92.73%   -0.01%     
==========================================
  Files         131      131              
  Lines       24445    24442       -3     
==========================================
- Hits        22671    22666       -5     
- Misses       1774     1776       +2     

Impacted Files	Coverage Δ
emmet-core/emmet/core/chemenv.py	97.75% <91.66%> (-2.25%)	⬇️
emmet-builders/emmet/builders/materials/chemenv.py	100.00% <100.00%> (ø)

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[JaGeo]

@munrojm Tests are passing. I am happy to hear what you think and I am also interested whether the builder now works on your systems and with your memory requirements etc.

[munrojm]

@JaGeo, thank you for these changes! This looks great. I am going to merge it now, and will get it running in our build pipeline tomorrow. I will update #595 once it is chugging along with any comments or concerns.