Here are my two favorite (bookmarked) links for packaging and developing for rust. The trick is keep packaging and rust development separate and use specific dev environment flakes. So for dev work just bring cargo and rust as the nativeBuildInputs in mkShell (and any non rust dependencies) and then use standard cargo for development. But for packaging use one of the fancy tools.
1. https://srid.ca/rust-nix
2. https://discourse.nixos.org/t/cargo2nix-dramatically-simpler...