Complete the function binary_strings(string: str) -> Generator[str, None, None]. binary_strings accepts a string of 0's, 1's, and X's and returns a generator that goes through all possible strings where the X's could be either 0's or 1's. For example with the string '0XX1', the possible strings are '0001', '0011' '0101', and '0111'. When generating the strings, the X's should first be replaced with 0's and then be replaced with 1's. Requirements:
You may NOT use anything from the itertools or functools modules. You must use the yield keyword in your solution. You must use recursion in this problem. binary_strings does not itself need to be recursive but you must use recursion in your solution.