Add all of iogamaster modules

modules/nixos/system/nix/default.nix

@@ -0,0 +1,66 @@
+{
+  options,
+  config,
+  pkgs,
+  lib,
+  ...
+}:
+with lib;
+with lib.frajul;
+let
+  cfg = config.system.nix;
+in
+{
+  options.system.nix = with types; {
+    enable = mkBoolOpt false "Whether or not to manage nix configuration.";
+    package = mkOpt package pkgs.nixVersions.latest "Which nix package to use.";
+    extraUsers = mkOpt (listOf str) [ ] "Extra users to trust";
+  };
+
+  config = mkIf cfg.enable {
+    environment.systemPackages = with pkgs; [
+      nil
+      nixfmt-rfc-style
+      nix-index
+      nix-prefetch-git
+    ];
+
+    nix =
+      let
+        users = [
+          "root"
+          config.user.name
+        ];
+      in
+      {
+        inherit (cfg) package;
+
+        settings =
+          {
+            experimental-features = "nix-command flakes";
+            http-connections = 50;
+            warn-dirty = false;
+            log-lines = 50;
+            sandbox = "relaxed";
+            auto-optimise-store = true;
+            trusted-users = users ++ cfg.extraUsers;
+            allowed-users = users;
+          }
+          // (lib.optionalAttrs config.apps.tools.direnv.enable {
+            keep-outputs = true;
+            keep-derivations = true;
+          });
+
+        gc = {
+          automatic = true;
+          dates = "weekly";
+          options = "--delete-older-than 7d";
+        };
+
+        # flake-utils-plus
+        generateRegistryFromInputs = true;
+        generateNixPathFromInputs = true;
+        linkInputs = true;
+      };
+  };
+}