Fixes: 1) Adjust `is_business` property logic for accuracy; 2) Fix import cleanup in serializers and utils files;
Extra: Refactor `core.models`, `core.utils`, and `core.vendors` for improved type annotations and other minor adjustments; Expand mypy exclusions in `pyproject.toml`.
Fixes: 1) Correct incorrect type annotations and imports for `readline` in `deepl_translate` command; 2) Remove unused variables `billing_address` and `shipping_address` in address application logic.
Extra: Add `# type: ignore` comments to suppress type-checking errors across admin classes.
Fixes: 1) Correct use of `@action` decorator within `ActivationActionsMixin` for defining admin actions; 2) Remove unused `BasicModelAdmin` inheritance from multiple admin classes.
Extra: Refactor and simplify admin imports and site registration for better readability and maintainability.
Fixes: 1) Remove 'recently_viewed' ManyToManyField from User model and related migration; 2) Correct handling of product addition in 'recently_viewed' logic.
Extra: Refactor 'recently_viewed' to use cache instead of database field; cleanup unused imports and model attributes.
