infra: tox -e coverage-check

[speller26]

Added a coverage-check testenv to tox.ini, so tox will now fail if coverage falls below 100%

Issue #, if available:

Description of changes:

Testing done:

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (4e0c0f2) to head (bfd566d).

Additional details and impacted files

@@            Coverage Diff            @@
##              main     #1353   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          171       171           
  Lines        11648     11648           
  Branches      1538      1538           
=========================================
  Hits         11648     11648           

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