input: Write a function to check if two strings are rotations of each other.
  assert is_rotation("abcde", "cdeab") == True
  assert is_rotation("abcde", "abced") == False
  assert is_rotation("waterbottle", "erbottlewat") == True
  assert is_rotation("hello", "lloeh") == False
output: def is_rotation(s1: str, s2: str) -> bool:
      if len(s1) != len(s2):
          return False
      return s2 in s1 + s1