input: Write a python function to scramble the characters of a given string.
  assert len(scramble_string("Hello World")) == len("Hello World")
  assert set(scramble_string("Hello World")) == set("Hello World")
  assert scramble_string("12345") != "12345"
output: import random
  
  def scramble_string(s):
      s_list = list(s)
      random.shuffle(s_list)
      return ''.join(s_list)