Provide prebuilt static executables

Part of #12 - it sounds like some users would appreciate downloadable prebuilt binaries.

I think we should be able to do this from the nix flake:

https://cs-syd.eu/posts/2024-04-20-static-linking-haskell-nix
https://github.com/nh2/static-haskell-nix

(more docs to read, etc)