Remove `with` and `rec`

with and rec are considered anti-patterns:

• with makes it unclear where variables are assigned and what variables refer to.

  Instead of with pkgs; [ foo ], write [ pkgs.foo ] directly.

• rec also makes it unclear what variables refer to and makes it easy to introduce subtle bugs.

  Instead of rec { a = 1; b = a; }, use a let binding:

  let a = 1; b = a; in { inherit a b; }

See: https://nix.dev/guides/best-practices