[chore] Tooling tweaks

[zerolab]

• tidy up tox.config (includes COVERAGE_CORE=sysmon for Python 3.12, which should keep tests speedy)
• use combined coverages from all tests
• add missing token for Codecov
• use uv to install deps
• run tox in quiet mode - less noise, minor speed bump in CI
• bump ruff to latest version

[codecov-commenter]

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.07%. Comparing base (cf12512) to head (b494736).
Report is 20 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #816      +/-   ##
==========================================
+ Coverage   92.83%   93.07%   +0.23%     
==========================================
  Files          47       47              
  Lines        4148     4144       -4     
  Branches      605      704      +99     
==========================================
+ Hits         3851     3857       +6     
+ Misses        176      173       -3     
+ Partials      121      114       -7     

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