Implement bank account with cashback

Implement a bank account processor. Given an initial non-negative integer balance B and a list of operations (n up to 1e 5), apply each operation in order and return the final balance. Operations are: ( 1) DEPOSIT x — add x to the balance; ( 2) WITHDRAW x — subtract x only if balance ≥ x, otherwise ignore the operation; ( 3) CASHBACK p — credit floor(balance * p / 100) to the balance. Assume all x and p are non-negative integers; use 64-bit integers to avoid overflow. Target O(n) time and O( 1) extra space. Provide unit tests for edge cases (zero amounts, multiple consecutive cashbacks, ignored withdrawals, large values). Example: B=100, ops=["DEPOSIT 50","WITHDRAW 120","CASHBACK 10","WITHDRAW 15"] → 18.