That's because the package is not available on Codewars.

You can see the list of installed packages on the Wiki. Feel free to request for a package by opening an issue on the codewars-runner-cli repository.

Thanks!
Should I be able to use permutations() from itertools::Itertools? (currently I can't)

Rust - for some reason it can't find the bit_set crate.
Rust playground have no such problem: https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=0fe557ff4e7f998f25235fa86af4a4bb