things I've changed from the PR:
- dropped legacy (i.e. non-flake) compat stuff, which turns out to account for most of the diff
- dropped `packages.garnet` since it doesn't work with `nix build .#garnet`
- back to using Rust-extended packages everywhere, which _seems_ fine
the rest is just re-inlining things and other refactors
final question:
it does seems a bit weird that `garnet-rs` arg to `project.nix` was always the same
might be a mistake, and we're supposed to be using local for local build?
"improve nix-haskell use"
there are a few things going on here but the main ones are ...
note that changes we keep are essentially:
- bumping `nix-haskell` to avoid shell hook workaround
- various changes in how we call `nix-haskell`
- using `libCgarnet_rs` name, which Cabal expects
- adding proper non-dev-shell targets, so that e.g. `nix run` works
