Add testing for Pydantic 1/2

[cthoyt]

This PR adds to the testing framework checks for compatibility with both Pydantic 1 and 2

[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (53b161d) 87.07% compared to head (25b9c5d) 87.38%.

❗ Current head 25b9c5d differs from pull request most recent head c9bb681. Consider uploading reports for the commit c9bb681 to get more accurate results

Files	Patch %	Lines
src/acsets/acsets.py	91.66%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #42      +/-   ##
==========================================
+ Coverage   87.07%   87.38%   +0.30%     
==========================================
  Files           6        6              
  Lines         325      325              
  Branches       54       54              
==========================================
+ Hits          283      284       +1     
  Misses         36       36              
+ Partials        6        5       -1     

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[olynch]

Let's figure out why the documentation is failing here, and then get this merged.

[olynch]

Going to merge this even if the doc-test is failing, because the documentation still builds.