GitHub Actions maintenance

[jayqi]

• Bumps several GitHub Actions versions.
• Drops Python 3.7 from CI. Adds Python 3.11 and 3.12.
• Switches to uv for installing packages in CI.
• Updates CLI test to use sys.executable instead of python so that the correct virtual environment is reliably used

Closes #172

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.80%. Comparing base (5a1883e) to head (20103c5).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #173   +/-   ##
=======================================
  Coverage   96.80%   96.80%           
=======================================
  Files           6        6           
  Lines         188      188           
=======================================
  Hits          182      182           
  Misses          6        6           

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[pjbull]

Thanks for digging in, this looks great.