Make species hash and coord hash optional in MoleculeMetadata

[Andrew-S-Rosen]

This PR closes #1149 by making the species hash and coord hash fields optional in MoleculeMetadata, only generating them if OpenBabel is installed. In return, it is possible to generate MoleculeMetadata without relying on OpenBabel.

An alternate approach was given in #1150 where I used JMolNN as a fallbak option in place of OpenBabelNN, but I feel like the current PR is more suitable because it might be difficult to debug a scenario where a change in the environment's dependencies yields a different hash.

To reiterate what I mention in the issue report, the motivation behind this PR is that OpenBabel is a really annoying dependency to require since it is not on PyPI. This means any workflow infrastructure wanting to rely on MoleculeMetadata must rely on the user to install OpenBabel from source or Conda unless this PR is merged.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 71.42857% with 2 lines in your changes missing coverage. Please review.

Project coverage is 90.41%. Comparing base (a705a61) to head (522c17c).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
emmet-core/emmet/core/structure.py	71.42%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1151      +/-   ##
==========================================
- Coverage   90.42%   90.41%   -0.01%     
==========================================
  Files         147      147              
  Lines       14448    14455       +7     
==========================================
+ Hits        13065    13070       +5     
- Misses       1383     1385       +2     

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[Andrew-S-Rosen]

Also, if approved, would it be possible to get a version release (or pre-release) after this PR? 🙏

[tsmathis]

Thanks @Andrew-S-Rosen, this seems reasonable. Happy to merge this in if you're satisfied?

Will also get a release out ASAP as well

[Andrew-S-Rosen]

Yup that'd be great!

[Andrew-S-Rosen]

Thank you, @tsmathis!!!

[tsmathis]

@Andrew-S-Rosen, we're working through a deployment for a full emmet release, but for now try using the 0.84.3rc6 pre-release and let us know if anything isn't working on your end!

[Andrew-S-Rosen]

Thanks! Seems to work!