Refactor(api_service): streamline API request handling and normalize data types

- Updated the `createUser` method for improved readability and consistency.
- Refactored normalization functions to return specific enum types for categories, severities, and statuses.
- Adjusted the handling of image uploads and location data to enhance clarity and maintainability.
- Changed the dependency type for the `http` package in `pubspec.lock` to reflect its direct usage.

pubspec.lock

@@ -262,7 +262,7 @@ packages:
     source: hosted
     version: "0.2.5"
   http:
-    dependency: transitive
+    dependency: "direct main"
     description:
       name: http
       sha256: bb2ce4590bc2667c96f318d68cac1b5a7987ec819351d32b1c987239a815e007