feat(ci): update build tooling

[WikiRik]

Updates the rollup version we use and introduces a separate build step in the CI so we test on the files that will also be published to npm. This also allows us to more easily update eslint in a future PR. It's a feat because there might be (very) minor changes to the build itself.

This incorporates part of the changes of #2401

Checklist

• PR contains only changes related; no stray files, etc.
• README updated (where applicable)
• Tests written (where applicable)
• References provided in PR (where applicable)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (f2b5c17) to head (a661988).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##            master     #2629   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          114       114           
  Lines         2566      2566           
  Branches       651       651           
=========================================
  Hits          2566      2566           

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[WikiRik]

Because I want to validate that the regression of #2630 does not happen here, I will put this in draft

[WikiRik]

I specified the target for compilation in a661988 (#2629) and manually validated that it does not introduce the same regression as #2630

[rubiin]

LGTM then