Setup code coverage tool

[fractalwrench]

Goal

Whilst code coverage isn't a perfect metric it is a useful tool for highlighting when parts of a codebase are missing tests entirely. Kover provides code coverage reports for both Kotlin/Java source code and allows generating either a HTML or XML file.

In this changeset I've applied Kover to all production modules and created an aggregate report that can be accessed with ./gradlew koverHtmlReport. This report produces a HTML file that can be accessed at build/reports/kover/html.

If there was desire to setup code coverage tracking it would be possible to create an XML report using ./gradlew koverXmlReport and upload it to a service such as codecov (what we use at Embrace). For now I feel it's just useful having this as an option to highlight code coverage locally rather than tracking things continuously.

[breedx-splk]

Having coverage is great! I think we'd want to be conservative about gating builds on it, but we definitely use codecov in the java core repo for PRs to help ensure that coverage isn't significantly declining (here's an example) and I think it's nice to demonstrate project maturity by having a badge on the main readme (like java core does). 🤘🏻

[breedx-splk]

Love it!

[LikeTheSalad]

Thank you!