Alter how version is determined

[munrojm]

This PR adds a fallback version based on what is populated in _version.py. This file will also be auto populated whensetuptools_scm can determine the version from the git history. This is intended to fix deployment issues where the API is installed without any access to the git tags.

[codecov-commenter]

Codecov Report

Merging #337 (c1473fc) into main (8122a76) will decrease coverage by 3.65%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #337      +/-   ##
==========================================
- Coverage   91.96%   88.31%   -3.66%     
==========================================
  Files          85       80       -5     
  Lines        3759     3397     -362     
==========================================
- Hits         3457     3000     -457     
- Misses        302      397      +95     

Impacted Files	Coverage Δ
emmet-core/emmet/core/thermo.py	57.14% <0.00%> (-37.50%)	⬇️
emmet-core/emmet/core/provenance.py	59.09% <0.00%> (-35.23%)	⬇️
emmet-core/emmet/core/mpid.py	68.51% <0.00%> (-25.93%)	⬇️
emmet-core/emmet/core/vasp/material.py	81.33% <0.00%> (-16.00%)	⬇️
emmet-core/emmet/core/structure.py	86.48% <0.00%> (-13.52%)	⬇️
emmet-core/emmet/core/electronic_structure.py	87.80% <0.00%> (-7.93%)	⬇️
emmet-core/emmet/core/vasp/validation.py	78.40% <0.00%> (-6.82%)	⬇️
emmet-core/emmet/core/settings.py	90.38% <0.00%> (-5.77%)	⬇️
emmet-core/emmet/core/utils.py	86.56% <0.00%> (-4.48%)	⬇️
emmet-core/emmet/core/vasp/task.py	97.40% <0.00%> (-2.60%)	⬇️
... and 6 more

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