Code Coverage for Tests

[JamesLMilner]

This adds nyc to the along module in order to see how it might work for getting information on code coverage. This could eventually close #2138 if we're happy with the approach.

Edit: This started as a proof of concept and I transitioned it to a full PR for adding Code Coverage to all packages

[rowanwins]

What is the intent with how we'd apply this @JamesLMilner ? Is there an automated test that checks if coverage is being improved or if it declines? Or is there are report that we'll be able to see via the checks above?

[JamesLMilner]

@rowanwins the aim here is that we firstly want to be able to see code coverage on push. Ideally we also want to be able to determine how it's changed between master. I'm working on adding another GitHub Action that will run coverage on the current branch and on master so you can compare the difference. I am looking to see if there's a way to write a script that will do a diff on the outputs somehow.

[JamesLMilner]

I think this should be fixed up now