Cross-compile to Scala 3

[nikololiahim]

• Revise dependencies
  • Drop nonEmpty (replace with cats.data.NonEmptyVector)
  • Drop cats-mtl, monix-newtypes (they are not used anywhere)
  • (Optional) Port tests to munit Migration to munit #27.
  • Update dependencies to latest versions.
• Configure compiler plugins (kind-project, better-monadic-for )
• Update CI to run tests with Scala 3.
• Publish new version.