[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 :white_check_mark:

Project coverage is 93.07%. Comparing base (cf12512) to head (b494736). Report is 14 commits behind head on main.

Additional details and impacted files

```diff @@ 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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