Introduce the sbt-explicit-dependencies

The plugin allows a strict definition of dependencies in the appropriate scope.

Update github actions workflows to check that no unused dependencies are added and that all used dependencies are explicitly declared.

https://github.com/cb372/sbt-explicit-dependencies

Start by reviewing the repository's GitHub Actions workflows and the linked sbt-explicit-dependencies plugin documentation. Configure the workflows to check that unused dependencies are rejected and all used dependencies are explicitly declared; done means both checks run successfully in GitHub Actions.

Written by the indexing model from the issue text.