Add CI workflow for JS unit tests

[priethor]

What

Improves the project's CI to run JS unit tests in PRs and pushes to trunk.

Why

JS unit tests were recently added to the project, so it's good that we run them as part of the CI.

How

• Adding a new GH workflow that runs on the minimum node version on PRs and node 20, 22, and 24 in trunk
• Upload the coverage report to codecov; adapt the other CI workflows to put the coverage reports in different subfolders, so that local runs don't overwrite each other

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 10.54%. Comparing base (0a774ff) to head (bfcf4e8).
⚠️ Report is 1 commits behind head on trunk.

Additional details and impacted files

@@             Coverage Diff              @@
##              trunk     #250      +/-   ##
============================================
- Coverage     10.97%   10.54%   -0.43%     
  Complexity     4284     4284              
============================================
  Files           266      279      +13     
  Lines         33139    34576    +1437     
============================================
+ Hits           3636     3645       +9     
- Misses        29503    30931    +1428     

Flag	Coverage Δ
e2e	29.55% <0.00%> (-0.03%)	⬇️
javascript	0.26% <100.00%> (?)
phpunit	6.06% <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.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

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Props priethor, cbravobernal.

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[cbravobernal]

Let's merge it.

[cbravobernal]

We may need it to rebase, as I fixed the Placeholder error a while ago.

[priethor]

Yes, this branch needs updating with trunk and fixing some tests yet, I'll do it to help with the coverage in #253 (although it should not be a blocker for that PR)

[priethor]

@cbravobernal the JS failing test is fixed now; feel free to manually test and rebase #253 🚀