fix: resolve AttributeError in User model and ensure consistent password handling

- Fixed the `AttributeError: 'User' object has no attribute '_password'` by properly mapping the `_password` attribute to the `password` column in the database.
- Updated the `User` model to ensure passwords are only hashed once during creation and not re-hashed when retrieved or updated.
- Improved the `check_password` method to correctly compare hashed passwords.
- Verified the signup and login flow to ensure consistent behavior

models/User/user.py

@@ -1,22 +1,23 @@
-from models import db
 from werkzeug.security import generate_password_hash, check_password_hash
+from models import db
 
 class User(db.Model):
     __tablename__ = 'users'
     
     id = db.Column(db.Integer, primary_key=True)
     username = db.Column(db.String(80), unique=True, nullable=False)
-    password = db.Column(db.String(128), nullable=False)
+    _password = db.Column("password", db.String(255), nullable=False)    
     
-    def __init__(self, username, password, hash_password=True):
-        self.username = username
-        if hash_password:
-            self.password = generate_password_hash(password, method="pbkdf2:sha256")
+    @property
+    def password(self):
+        return self._password
+
+    @password.setter
+    def password(self, raw_password):
+        if not raw_password.startswith("pbkdf2:sha256:"):
+            self._password = generate_password_hash(raw_password)
         else:
-            self.password = password
+            self._password = raw_password
 
     def check_password(self, password):
-        return check_password_hash(self.password, password)
-    
-    def __repr__(self):
-        return f"<User {self.username}>"
+        return check_password_hash(self._password, password)