input: Write a function to find the length of the longest word in a given string.
  assert longest_word_length("The quick brown fox jumps over the lazy dog") == 5
  assert longest_word_length("Python is an amazing programming language") == 11
  assert longest_word_length("A journey of a thousand miles begins with a single step") == 8
output: def longest_word_length(s):
      words = s.split()
      return max(len(word) for word in words)