input: Write a python function to count the number of numeric characters in a list of strings.
  assert count_numbers(['a', '1', 'b', '2', 'c', '3']) == 3
  assert count_numbers(['123', 'abc', '456']) == 6
  assert count_numbers(['', ' ', 'a', '1']) == 1
output: def count_numbers(strings):
      count = 0
      for string in strings:
          for char in string:
              if char.isdigit():
                  count += 1
      return count