add new external flake to provide helper functions

flake.lock

@@ -180,6 +180,26 @@
         "type": "gitlab"
       }
     },
+    "helpers": {
+      "inputs": {
+        "nixpkgs": [
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1788016189,
+        "narHash": "sha256-O57BYyiEsgdQAluguEWMQtkog5puR2JjUx4+A1br7Q0=",
+        "ref": "refs/heads/main",
+        "rev": "6bb0221b270bf8a54c4efe646e8ec39d74e55f9f",
+        "revCount": 4,
+        "type": "git",
+        "url": "https://git.greyweather.dev/greyweather/nix-helper-flake"
+      },
+      "original": {
+        "type": "git",
+        "url": "https://git.greyweather.dev/greyweather/nix-helper-flake"
+      }
+    },
     "home-manager": {
       "inputs": {
         "nixpkgs": [
@@ -315,6 +335,7 @@
       "inputs": {
         "firefox-addons": "firefox-addons",
         "flake-parts": "flake-parts",
+        "helpers": "helpers",
         "home-manager": "home-manager",
         "import-tree": "import-tree",
         "nh": "nh",