input: Write a python function to convert a number to its individual digits.
  assert number_to_digits(12345) == [1, 2, 3, 4, 5]
  assert number_to_digits(67890) == [6, 7, 8, 9, 0]
  assert number_to_digits(10203) == [1, 0, 2, 0, 3]
output: def number_to_digits(number):
      return [int(digit) for digit in str(number)]