Identify a suitable test coverage checker

[mxdvl]

Is your feature request related to a problem? Please describe. Currently, the @guardian/libs coverage is pointing to the now-archived repo.

Describe the solution you'd like I would like up-to-date coverage reports to be available and badges to work.

Describe alternatives you've considered We can build our own coverage report if we do not want to rely on external tools such as coveralls.