Secure registration and add login with and without OTP

[Vianpyro]

Description

This pull request introduces significant improvements to the user authentication and registration system. The registration flow now enforces email verification before user creation and supports 2FA (OTP). Various code enhancements were made for clarity, consistency, and maintainability.

Changes Made

• Refactored user registration to use PostgreSQL stored procedure and sanitize username input.
• Replaced UserCreate schema with UserRegister for clarity and alignment with the new flow.
• Moved sanitize_username to string_utils and removed username.py.
• Added HTTPException handling for existing users during registration.
• Added descriptive docstring to the user registration endpoint.
• Renamed language_id to language_iso_code in the User model for clarity.
• Renamed language_iso_code to language_id in model and schema for consistency.
• Implemented email confirmation flow and login endpoint.
• Enhanced login endpoint with improved response structure.
• Implemented OTP-based 2FA login and registration enhancements for OTP secret generation.
• Moved in-memory store declaration to a more appropriate location for clarity.
• Updated SQLAlchemy engine initialization for better performance (echo=False, pool_pre_ping=True).
• Changed registration flow to require email confirmation before creating the user account.

How to Test

1. Register a new user using the registration endpoint.
2. Check your email for a confirmation link and confirm the account.
3. Attempt to log in using the confirmed account credentials.
4. If 2FA is enabled, provide the OTP when prompted.
5. Verify that the login flow completes successfully and that invalid or unconfirmed users are appropriately blocked.

Checklist

• My code follows the project's coding style.
• I have performed a self-review of my code.
• I have added necessary tests (if applicable).
• I have documented my changes (if necessary).

Additional Context

These updates are foundational for enforcing stronger security in the authentication process, including email verification and 2FA. The code has been refactored to improve modularity and clarity, especially in schema and utility functions.