Fall back to JMolNN if open babel is not installed when generating MoleculeMetadata

[Andrew-S-Rosen]

Closes #1149.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 33.33333% with 6 lines in your changes missing coverage. Please review.

Project coverage is 72.57%. Comparing base (a705a61) to head (f2b6450).

Files with missing lines	Patch %	Lines
emmet-core/emmet/core/utils.py	33.33%	6 Missing ⚠️

❗ There is a different number of reports uploaded between BASE (a705a61) and HEAD (f2b6450). Click for more details.

HEAD has 4 uploads less than BASE

Flag	BASE (a705a61)	HEAD (f2b6450)
	6	2

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #1150       +/-   ##
===========================================
- Coverage   90.42%   72.57%   -17.86%     
===========================================
  Files         147       77       -70     
  Lines       14448     5105     -9343     
===========================================
- Hits        13065     3705     -9360     
- Misses       1383     1400       +17     

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