Sometimes it is useful to break a number into digits, transform each digit, and then build a new number from the result. Write square_digits, which takes a non-negative number num, squares each of its digits, joins those squared values together, and returns the result as a number. For example, the digits 9, 1, 1, 9 become 81, 1, 1, 81.

def square_digits(num: int) -> int: