carnix has been archived on github and shows up as notf ound on pijul, the author (@P-E-Meunier) seems to be mostly dormant on github as well.
carnix and crateIO hasn't seen an update in nixpkgs since 2019 (carnix.nix, crates-io.nix), and there have been alternatives that are more maintained.

Related issue: #57235, perhaps we can combine these two into one

Remaining dependents There should be no remaining dependents:

• cargo-download
• toml2nix