Fixes: 1) Correct unnecessary use of `Collection` type hint in core and simple serializers; 2) Fix translation of "blacklisted tokens" in Russian localization;
Extra: 1) Simplify conditional logic in `get_children` methods across serializers; 2) Remove unused imports and improve code readability.
Fixes: 1) Corrected `ForeignKey` type assertions across models; 2) Resolved typos and formatting inconsistencies in `.env` and README; 3) Fixed explicit boolean checks in user manager methods.
Extra: Updated type hints in multiple models, serializers, and views.
