Fixes: 1) Resolve annotations compatibility with mypy `type: ignore` adjustments; 2) Correct `resolve_price_with_currency` method to ensure proper float returns; 3) Handle scenarios for empty or null queryset in vendor methods.
Extra: 1) Refactor utility functions for better type annotations and robustness; 2) Minor formatting corrections and removal of redundant mypy strict setting; 3) Improve method return types for consistency.
