Added nix files and updated helpers library for dart 3

pubspec.yaml

@@ -37,7 +37,10 @@ dependencies:
   cupertino_icons: ^1.0.2
   dio: ^5.2.1+1
   flutter_riverpod: ^2.1.3
-  helpers: ^1.2.0
+  helpers:
+    git:
+      url: https://github.com/mitch2na/helpers.git
+      ref: main
   uuid: ^3.0.7
   json_annotation: ^4.8.0
   shared_preferences: ^2.1.2
@@ -105,4 +108,4 @@ icons_launcher:
       adaptive_foreground_image: "assets/app_icon1.png"
       adaptize_round_image: "assets/app_icon_round.png"
     ios:
-      enable: true
+      enable: true