Switch to nixica 0.1.0

Summary

• Migrate from flake-parts/import-tree/treefmt-nix to nixica 0.1.0
• Move modules/ content into nix/ with import-tree patterns
• Replace test flake's get-flake/flake-parts/import-tree/treefmt-nix with nixica
• Use path input for werrorwolf in test instead of get-flake

Closes #1 (closed)

@locallycompact