input: Write a function to find the character with the maximum frequency in a given string.
  assert max_frequency_char("aabbbcccc") == 'c'
  assert max_frequency_char("hello world") == 'l'
  assert max_frequency_char("python programming") == 'g'
output: def max_frequency_char(s: str) -> str:
      from collections import Counter
      frequency = Counter(s)
      max_char = max(frequency, key=frequency.get)
      return max_char