input: Write a function to find the length of the longest number in a list.
  assert find_longest([123, 5, 4567, 89, 0]) == 4
  assert find_longest([1, 22, 333, 4444, 55555]) == 5
  assert find_longest([100, 1000, 10, 10000]) == 5
output: def find_longest(numbers):
      return max(len(str(number)) for number in numbers)