fix(phpstan): address issues with product price calculation and caching

This commit addresses two issues in the product model and utilities.

1) In the product model, changes are made to ensure that the cacheName variable is given a default
value of false and is later checked to be not false in the if condition. This ensures that we don't
end up writing null data to the cache.

2) Changes are made in the getPriceFieldForProduct function to fix some potential issues with price
calculations. Minor refactor includes:

- Added a check to ensure the getOption method exists before calling it, to prevent potential fatal
errors.
- Defaulted currencyPrices to an empty array to prevent potential PHP warnings when trying to
access array keys on a null value.
- Updated the return statement new QUI\\ERP\\Money\\Price to exclude currencyPrices which was
causing issues.