input: Write a python function to find the cumulative sum of the digits of a number.
  assert cumulative_sum_of_digits(12345) == 15
  assert cumulative_sum_of_digits(9876) == 30
  assert cumulative_sum_of_digits(1001) == 2
output: def cumulative_sum_of_digits(number):
      return sum(int(digit) for digit in str(number))