chore: refactor system modules

system/packages/nix.nix

@@ -0,0 +1,49 @@
+{
+  lib,
+  config,
+  ...
+}:
+with lib; let
+  cfg = config.system.packages.nix;
+in {
+  options.system.packages.nix = {
+    allowUnfree = mkEnableOption "Enable unfree packages";
+    disableSandbox = mkEnableOption "Disable Nix sandbox";
+    gc = {
+      automatic = mkOption {
+        type = types.bool;
+        default = true;
+      };
+      dates = mkOption {
+        type = types.str;
+        default = "Monday 01:00 UTC";
+      };
+      options = mkOption {
+        type = types.str;
+        default = "--delete-older-than 30d";
+      };
+    };
+    nix-ld.enable = mkEnableOption "Enable unpatched binaries support";
+    trusted-users = mkOption {
+      type = types.listOf types.str;
+      example = ["alice" "bob"];
+      default = [];
+    };
+  };
+
+  config = {
+    nix = {
+      inherit (cfg) gc;
+      settings = {
+        inherit (cfg) trusted-users;
+        sandbox = cfg.disableSandbox;
+        experimental-features = ["nix-command" "flakes"];
+        auto-optimise-store = true;
+      };
+    };
+    nixpkgs.config.allowUnfree = true;
+    programs = {
+      inherit (cfg) nix-ld;
+    };
+  };
+}