feat(modules): move nix settings to a seperate module

modules/nixos/common-nix-conf.nix

@@ -0,0 +1,51 @@
+{ config, lib, pkgs, ... }:
+
+let
+  inherit (lib) mkIf mkEnableOption mkOption types;
+
+  cfg = config.commonSettings.nix;
+in
+{
+  options.commonSettings.nix = {
+    enable = mkOption {
+      default = true;
+      type = types.bool;
+    };
+    enableMirrors = mkEnableOption "cache.nixos.org mirrors in Mainland China";
+  };
+
+  config = mkIf cfg.enable {
+    nix.package = pkgs.nixVersions.latest;
+
+    nix.gc = {
+      automatic = true;
+      dates = "weekly";
+      options = "--delete-older-than 30d";
+    };
+
+    nix.optimise.automatic = true;
+
+    nix.settings = {
+      experimental-features = [ "nix-command" "flakes" ];
+      auto-optimise-store = true;
+      trusted-users = [ "root" ];
+
+      substituters = [
+        "https://nix-community.cachix.org"
+        "https://cache.garnix.io"
+      ];
+
+      extra-substituters = mkIf cfg.enableMirrors [
+        "https://mirrors.bfsu.edu.cn/nix-channels/store"
+        "https://mirrors.ustc.edu.cn/nix-channels/store"
+      ];
+
+      trusted-public-keys = [
+        "cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY="
+        "nix-community.cachix.org-1:mB9FSh9qf2dCimDSUo8Zy7bkq5CX+/rkCWyvRCYg3Fs="
+        "cache.garnix.io:CTFPyKSLcx5RMJKfLo5EEPUObbA78b0YQ2DTCJXqr9g="
+      ];
+    };
+  };
+}
+

modules/nixos/default.nix

@@ -1,6 +1,7 @@
 { config, pkgs, ... }:
 {
   imports = [
+    ./common-nix-conf.nix
     ./restic.nix
     ./vaultwarden.nix
     ./prometheus.nix