Fix CI pipeline

[zainab-ali]

This ~almost~ fixes the CI pipeline.

• Updates the scalafmt config.
• Adds type parameters to make Scala 2.12 happy.
• Removes unused imports.
• Adds scalac-compat-annotation and a load of unused annotations.
• Adds junit as a scaladoc dependency for coreCats.

I'm hesitant to eagerly remove unused parameters as I don't have the context as to why they're there. If you'd like any removed, drop a comment next to them.

~The only outstanding issue is doc generation and the RunWith annotation. This is likely a scaladoc / tasty bug and needs a bit more investigation.~

[zainab-ali]

We're all green! I'm happy with merging.