This relies on Cargo2Nix, and because we don't want to be maintaining
that file by hand, we introduce a new continuous workflow to
automatically update the generated Cargo.nix and submit a PR whenever
something is merged into master.
This should make the process of supporting Nix bearable. We'll
re-assess in a while.
Co-authored-by: KtorZ <matthias.benkort@gmail.com>
