style: Switch to nixfmt from nixpkgs-fmt

Most of the ecosystem has moved to this formatter,
and many people configured their editors to autoformat it with this formatter.

Closes: https://git.snix.dev/snix/snix/issues/62
Change-Id: Icf39e7836c91fc2ae49fbe22a40a639105bfb0bd
Reviewed-on: https://cl.snix.dev/c/snix/+/30671
Reviewed-by: Florian Klink <flokli@flokli.de>
Tested-by: besadii
Autosubmit: Ilan Joselevich <personal@ilanjoselevich.com>

ops/machines/snix-cache/default.nix

@@ -1,18 +1,24 @@
-{ depot, pkgs, lib, ... }: # readTree options
+{
+  depot,
+  pkgs,
+  lib,
+  ...
+}: # readTree options
 { config, ... }: # passed by module system
 
 let
-  srvos =
-    import (builtins.fetchTarball {
+  srvos = import (
+    builtins.fetchTarball {
       url = "https://github.com/nix-community/srvos/archive/8e7d3c690975ee6790926bdfd1258016c967d163.tar.gz";
       sha256 = "sha256-l7epHqAcg8Qktu8vO2ZfjSH1wcai01XQOKQA9ADHIk4=";
-    });
-  disko =
-    (builtins.fetchTarball {
+    }
+  );
+  disko = (
+    builtins.fetchTarball {
       url = "https://github.com/nix-community/disko/archive/84dd8eea9a06006d42b8af7cfd4fda4cf334db81.tar.gz";
       sha256 = "13mfnjnjp21wms4mw35ar019775qgy3fnjc59zrpnqbkfmzyvv02";
-    });
-
+    }
+  );
 
 in
 {
@@ -38,7 +44,6 @@ in
       forceSSL = true;
     };
 
-
     security.acme.acceptTerms = true;
     security.acme.defaults.email = "admin+acme@numtide.com";
 
@@ -48,11 +53,9 @@ in
 
     systemd.network.networks."10-uplink".networkConfig.Address = "2a01:4f9:3071:1091::2/64";
 
-
     # Enable SSH and add some keys
     services.openssh.enable = true;
 
-
     users.users.root.openssh.authorizedKeys.keys =
       depot.ops.users.edef
       ++ depot.ops.users.flokli