The Nix code is taken from the Crane docs, and adapted for merging with the existing Haskell.Nix flake. The other files are from `cargo init`, with minor modifications, and `cargo generate-lockfile`.
The default dev shell contains tools for both languages.
We can now run `nix build .#rust` and `nix build .#haskell`, where the latter was previously `nix build .#aoc:exe:aoc`.