Leveling Up - Refactoring and re-use

file to edit: https://github.com/haskell/cabal-userguide/blob/main/src/leveling_up/01_refactoring_and_re-use.md

## Brief Summary

The motivation for this chapter is to show ways that common blocks in `.cabal` files can be factored out using common stanzas.

## Resources

[Old cabal user guide common stanza intro](https://cabal.readthedocs.io/en/3.4/developing-packages.html#modules-imported-from-other-packages)
[Old cabal user guide common stanza reference](https://cabal.readthedocs.io/en/3.4/cabal-package.html#common-stanzas)