refactor: Introduce utility functions for exception handling and database operations; update auth and playlist services to use new exception methods

tests/repositories/test_user.py

@@ -11,6 +11,7 @@ from app.models.plan import Plan
 from app.models.user import User
 from app.repositories.user import UserRepository
 from app.utils.auth import PasswordUtils
+from app.utils.database import create_and_save
 
 
 class TestUserRepository: