input: Write a python function to convert a given string to an array of characters.
  assert convert_to_char_array("Hello World!") == ['H', 'e', 'l', 'l', 'o', ' ', 'W', 'o', 'r', 'l', 'd', '!']
  assert convert_to_char_array("Python") == ['P', 'y', 't', 'h', 'o', 'n']
  assert convert_to_char_array("123456") == ['1', '2', '3', '4', '5', '6']
  assert convert_to_char_array("") == []
output: def convert_to_char_array(s):
      return list(s)