Add pre-commit hooks for nixfmt, deadnix, and statix

Also, exclude .pre-commit-config.yaml from SOPS processing

modules/shared/nixos/flatpaks.nix

@@ -1,5 +1,4 @@
-{ ... }:
-{
+_: {
   services = {
     flatpak = {
       enable = true;

modules/shared/nixos/internationalisation.nix

@@ -1,5 +1,4 @@
-{ ... }:
-{
+_: {
   # Select internationalisation properties.
   i18n = {
     defaultLocale = "en_US.UTF-8";

modules/shared/nixos/nixroutes.nix

@@ -1,6 +1,6 @@
 { config, lib, ... }:
 let
-  hostName = config.networking.hostName;
+  inherit (config.networking) hostName;
 in
 {
   programs.zsh.shellAliases.nixroutes = "cd ~/repos/dots && echo '=== Current Routes ===' && ip route show && ip -6 route show && echo '' && echo '=== New Build Routes ===' && nix eval --json '.#nixosConfigurations.${hostName}.config.systemd.network.networks.\"10-wan\".routes'";