style: Apply nixpkgs-fmt and fix

Apply standard formatting and some statix conventions using;

```sh
nixpkgs-fmt **.nix && statix fix .
```

With the intent of making contribution a bit easier and reducing mental
load in hand formatting (in the same vein as [black]).

[black]: https://github.com/psf/black#the-uncompromising-code-formatter

tests/lib.nix

@@ -17,7 +17,7 @@
     , testBoot ? true # if we actually want to test booting or just create/mount
     }:
     let
-      lib = pkgs.lib;
+      inherit (pkgs) lib;
       makeTest' = args:
         makeTest args {
           inherit pkgs;