ci: run unit tests on supported os runners

[zimeg]

Changelog

N/A - Testing changes.

Summary

This PR attempts to resolve issues noted in #462 using logs of CI from these changes 🧪

We hope to add unit test checks for all supported OS:

• Mac
• Linux (Ubuntu)
• Windows

Requirements

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 70.99%. Comparing base (24c1d2c) to head (2451d95).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #464      +/-   ##
==========================================
+ Coverage   70.96%   70.99%   +0.02%     
==========================================
  Files         220      220              
  Lines       18466    18466              
==========================================
+ Hits        13105    13110       +5     
+ Misses       4183     4178       -5     
  Partials     1178     1178              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

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

[zimeg]

Adjacent change worth coordinating with: #652 (the Pscx Expand-Archive fix for #651) also edits .github/workflows/tests.yml — it adds an install-tests matrix across macos-latest / ubuntu-latest / windows-latest and splits it out of the lint-test job. Since this PR is adding OS-matrix coverage to the same file, the two will want to rebase on each other rather than land independently.

One concrete signal from #652 that's relevant here: the Windows runner does run CI fine, but the installer's post-install courtesy check hangs under pwsh 7 on the current windows-latest image (the native-command _fingerprint | Tee-Object -Variable | Out-Null pipeline blocks with no console). #652 works around it with a static AST guard rather than a live install. Worth keeping in mind if the Windows unit-test leg here ends up shelling anything similar — the runner is viable, but native-command pipelines that expect a console are the sharp edge.