Keep an eye out for better doctest approaches

In #107, we got rid of our custom setup, and tests are now run via `cabal doctest`. We would prefer something that worked with `cabal test`, as well as Stack, Nixpkgs and Haskell.Nix's native testing approaches.

It's likely that the solution will involve the new "setup hooks" (https://github.com/haskell/cabal/pull/9551).

See #82 and #129 for more context.

Read issues #107, #82, and #129 for the existing doctest setup and context, then review Cabal's setup hooks, including PR #9551. Compare how doctests could work with cabal test, Stack, Nixpkgs, and Haskell.Nix native testing approaches. Done means a documented approach that integrates with those testing workflows.

Written by the indexing model from the issue text.