Revert "Remove py36 references"

[ewanek1]

Begins to resolve Issue 603. This PR removes all explicit references and workarounds for Python 3.6 across the codebase and documentation to support minimum Python version 3.7+.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.96%. Comparing base (347cb5e) to head (e444ff9).
Report is 1 commits behind head on main.

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1331   +/-   ##
=======================================
  Coverage   90.96%   90.96%           
=======================================
  Files         222      222           
  Lines        7501     7501           
=======================================
  Hits         6823     6823           
  Misses        678      678           

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