Refactor code structure; improve organization and readability across multiple files

models/users.py

@@ -34,3 +34,14 @@ class User(db.Model):
     def __repr__(self):
         return f"<User(id={self.id}, first_name={repr(self.first_name)}, last_name={repr(self.last_name)}, " \
                f"location={repr(self.location)}, staff={self.staff}, active={self.active})>"
+    
+    def serialize(self):
+        return {
+            'id': self.id,
+            'first_name': self.first_name,
+            'last_name': self.last_name,
+            'location_id': self.location_id,
+            'supervisor_id': self.supervisor_id,
+            'staff': self.staff,
+            'active': self.active
+        }