The `validators.py` file, containing user-related validation logic, has been moved from the core project directory to the `user` application directory.

This commit introduces a new test suite for the password validation logic in `user/validators.py`.

The tests cover all existing validator classes:
- `UppercaseValidator`
 - `LowercaseValidator`
 - `NumericValidator`
 - `SpecialCharacterValidator`
 - `AsciiValidator`

Each validator is tested for successful validation, failure cases with appropriate error messages, and correct help text generation. This ensures the reliability and correctness of the password validation system.

This commit introduces several refactoring improvements across the codebase to enhance clarity, remove redundancy, and simplify complex logic.

Key changes include:
- **PromoManager:** Simplified the filtering logic for promo codes by restructuring the query conditions for age and country, making it more readable.
- **Promo Model:** Streamlined property methods (`is_available`, `get_available_unique_codes`) for better readability and  consistency.
- **Serializers (`business`, `core`, `user`):**
- Removed unnecessary validation checks that are already handled by Django Rest Framework's default behavior (e.g., required fields).
- Simplified complex conditional logic and improved handling of query parameters (`MultiCountryField`).
- Made user-context checks in `BaseUserPromoSerializer` more direct and less defensive, assuming an authenticated request  context.
- **Settings:** Updated paths for password validators to reflect their new location in the `user` application.