Resolve "Improve CI by using Nix" ✨️

Closes #115 🐔️👍️
Approved-by: loutr <l.ta-ma@proton.me>

🦀️🍰🦀️🍰🦀️🍰

* fix(coverage): Generate format directly with one Nix invocation

* fix(atty): Remove unmaintained atty crate

* feat(ci): Use crane to perform tests

* chore(cargo-deny): Bump to latest syntax

* chore(nix): Use crane and fenix

* chore(rustfmt): Bump to 1.7.0

* chore(cargo): Bump dependencies

* chore(ci): Upgrade coverage tool

* chore(nix): Remove docker + devshell

* chore(ci): Use Nix instead of extern Docker images

* chore: Bump Nix to 23.11

* chore: Bump clippy to 1.80 nightly

* chore: Bump Rust to 1.80 nightly