Implement better CI

Our current CI script is less featureful than the ones provided by either the Stackage documentation or the `haskell-ci` platform. This has allowed build failures to sneak through that should not.

Inspect the repository's current CI script first, then compare its coverage with the CI features described in the Stackage documentation and provided by haskell-ci. Identify which build failures are currently missed and define the CI improvements and checks needed to prevent them.

Written by the indexing model from the issue text.