OPT: (memory) cache schema files upon first read from github

[yarikoptic]

Transpired by looking at never finalized

• Statically bundle dandi/schema json #155

as a much less intrusive and simpler approach to avoid repetitive requests for the same schema files.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (a9d7f89) 97.71% compared to head (e780174) 97.72%.
Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #213   +/-   ##
=======================================
  Coverage   97.71%   97.72%           
=======================================
  Files          17       17           
  Lines        1752     1755    +3     
=======================================
+ Hits         1712     1715    +3     
  Misses         40       40           

Flag	Coverage Δ
unittests	97.72% <100.00%> (+<0.01%)	⬆️

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[yarikoptic]

FWIW restarted for errored out windows

================================== FAILURES ===================================
____________________________ test_datacite[000008] ____________________________
dandischema\tests\test_datacite.py:156: in test_datacite
    datacite_post(datacite, meta.doi)
dandischema\tests\test_datacite.py:30: in datacite_post
    rp.raise_for_status()
.tox\py\Lib\site-packages\requests\models.py:1021: in raise_for_status
    raise HTTPError(http_error_msg, response=self)
E   requests.exceptions.HTTPError: 422 Client Error: Unprocessable Entity for url: https://api.test.datacite.org/dois

---------- coverage: platform win32, python 3.11.7-final-0 -----------
Coverage XML written to file coverage.xml

[yarikoptic]

was approved, so let's proceed