With a few exceptions for `lib.stylix` functions.
Once these exceptions are removed, we will have solved the issue with
NixOS's documentation.nixos.includeAllModules option.
See https://github.com/nix-community/stylix/issues/98
We don't actually need fully blown NixOS or home-manager configurations
just to read the declared `options`.
Instead, we can directly call `lib.evalModules` to build a minimal
configuration containing only stylix modules.