Adopt nixify across repos and use consistent Rust CI

[rvolosatovs]

https://github.com/rvolosatovs/nixify is already used in enarx, steward, drawbridge, benefice and vfs.
If we adopted the library in all Rust projects, then we could have a CI setup like in https://github.com/enarx/vfs/tree/main/.github/workflows, which would enable dependabot, automatic updates, cargo fmt, cargo clippy and cargo nextest on Linux and MacOS runners run via nix (and so using a locked-in rust toolchain version) with caching

#28 (comment)