Drop support for python 3.7, add testing for python 3.10

[charlesbluca]

This PR follows Dask's dropping of python 3.7 support and migration to supporting 3.10 by doing the same here.

[codecov-commenter]

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.09%. Comparing base (6c7c761) to head (ac143f1).
Report is 367 commits behind head on main.

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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #383      +/-   ##
==========================================
+ Coverage   88.94%   89.09%   +0.14%     
==========================================
  Files          68       68              
  Lines        3337     3337              
  Branches      653      657       +4     
==========================================
+ Hits         2968     2973       +5     
+ Misses        298      288      -10     
- Partials       71       76       +5     

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