Simplify codecov actions

[c-randall]

Description

Tie in nox to codecov workflow. New -- codecov argument for the nox session is used for this purpose. This keeps commands together in one conventient location rather than spread across many workflows/files.

Type of change

• New feature (non-breaking change which adds functionality)
• Optimization (back-end change that improves speed/readability/etc.)
• Bug fix (non-breaking change which fixes an issue)
• Chore (any other clean up, maintenance, etc.)

Key checklist:

• No style issues: $ nox -s linter [-- format]
• Code is free of misspellings: $ nox -s codespell [-- write]
• All tests pass: $ nox -s tests
• Badges are updated: $ nox -s badges

Further checks:

• The documentation builds: $ nox -s docs.
• Code is commented, particularly in hard-to-understand areas.
• Tests are added that prove fix is effective or that feature works.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 30.09%. Comparing base (d5f6997) to head (abc655b).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #22   +/-   ##
=======================================
  Coverage   30.09%   30.09%           
=======================================
  Files          40       40           
  Lines        1738     1738           
=======================================
  Hits          523      523           
  Misses       1215     1215           

Flag	Coverage Δ
unittests	30.09% <ø> (ø)

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🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.