input: Write a python function to check if all characters in a string are unique.
  assert are_all_characters_unique("Hello") == False
  assert are_all_characters_unique("abcdef") == True
  assert are_all_characters_unique("12345") == True
  assert are_all_characters_unique("112233") == False
output: def are_all_characters_unique(s):
      return len(s) == len(set(s))