fix: use `nixfmt` package for post-25.11 Nixpkgs

fix: add `cargoBuildFlags` to clippy check

feat: passthrough `cargo{Build,Test}Flags`

feat: infer `meta.homepage` from cargo manifest

feat: add `systems` option

feat: allow configuring completions arguments

fix: add clippy, rustfmt configs to fileset

refactor: flake outputs as separate option

feat: infer name and meta from Cargo.toml

feat: add tests to default src, option to override

init