chore: add code coverage

[stijnmoreels]

Add code coverage reporting.

Relates to arcus-azure/arcus#264

[netlify]

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[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (main@f524607). Click here to learn what that means.
Patch has no changes to coverable lines.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #518   +/-   ##
=======================================
  Coverage        ?   86.53%           
=======================================
  Files           ?       77           
  Lines           ?     3246           
  Branches        ?      220           
=======================================
  Hits            ?     2809           
  Misses          ?      360           
  Partials        ?       77           

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