some minor fixes

system/modules/nix/nh/default.nix

@@ -0,0 +1,33 @@
+{
+  config,
+  lib,
+  ...
+}: let
+  inherit (lib) mkIf mkEnableOption mkOption;
+  cfg = config.modules.nix.nh;
+in {
+  options = {
+    modules.nix.nh = {
+      enable = mkEnableOption "Enables nix helper";
+      clean = {
+        enable = mkEnableOption "Enables nix helper cleaning";
+        extraArgs = mkOption {
+          type = lib.types.str;
+          description = "Extra arguments for the clean command";
+          default = "";
+        };
+      };
+    };
+  };
+  config = mkIf cfg.enable {
+    programs = {
+      nh = {
+        enable = cfg.enable;
+        clean = {
+          enable = cfg.clean.enable;
+          extraArgs = cfg.clean.extraArgs;
+        };
+      };
+    };
+  };
+}