Add a new function `resolve_fiat_offer_price_for_user` to determine the correct offer price for users based on their subscription choices and any applicable discounts. Update payment handlers for CryptoPay, FreeKassa, Platega, SeverPay, and YooKassa to utilize this function, ensuring callback price validation and improving error handling for price mismatches. This enhances security by preventing callback payload tampering and ensures accurate pricing for users.