Enhance Security and Username Uniqueness for User Account

[Powan55]

As part of improving the security of user account creation and ensuring data integrity, we need to address the following tasks:

• [x] Password Hashing: Implement a password hashing mechanism to securely store user credentials in the database. Passwords should be salted and hashed before being stored, enhancing the protection of sensitive user information.

• [x] Username Uniqueness Check: Add functionality to check the database for duplicate usernames during the account creation process. Ensure that each user is assigned a unique username to prevent conflicts and confusion.

[Powan55]

Username Uniqueness was completed under issue #13