input: Write a python function to convert a comma-separated string of numbers into a list of integers.
  assert convert_to_int_list('1,2,3,4,5,6') == [1, 2, 3, 4, 5, 6]
  assert convert_to_int_list('10,20,30,40') == [10, 20, 30, 40]
  assert convert_to_int_list('7,14,21,28,35') == [7, 14, 21, 28, 35]
output: def convert_to_int_list(s):
      return list(map(int, s.split(',')))