New EmmetBaseModel

[shyamd]

This PR adds a new EmmetBaseModel for documents to inherit from so that certain fields are always present at the top level. This is recommended for top-level document models and not for sub-fields.

[codecov-commenter]

Codecov Report

Merging #235 (9060dfc) into main (33d002c) will increase coverage by 0.04%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #235      +/-   ##
==========================================
+ Coverage   91.54%   91.58%   +0.04%     
==========================================
  Files          40       41       +1     
  Lines        2791     2805      +14     
==========================================
+ Hits         2555     2569      +14     
  Misses        236      236              

Impacted Files	Coverage Δ
emmet-core/emmet/core/base.py	100.00% <100.00%> (ø)
emmet-core/emmet/core/optimade.py	90.19% <100.00%> (+0.19%)	⬆️
emmet-core/emmet/core/structure.py	100.00% <100.00%> (ø)
emmet-core/emmet/core/structure_group.py	95.32% <100.00%> (ø)
emmet-core/emmet/core/stubs.py	100.00% <100.00%> (ø)
emmet-core/emmet/core/task.py	100.00% <100.00%> (ø)
emmet-core/emmet/core/vasp/validation.py	85.88% <100.00%> (+0.16%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 33d002c...9060dfc. Read the comment docs.