input: Write a function to convert a given string to a list of integers.
  
  def to_int_list(s):
      return [int(x) for x in s.split(',')]
  assert to_int_list("1,2,3,4,5")==[1, 2, 3, 4, 5]
  assert to_int_list("10,20,30")==[10, 20, 30]
  assert to_int_list("4,8,15,16,23,42")==[4, 8, 15, 16, 23, 42]
  assert to_int_list("2,4,6,8")==[2, 4, 6, 8]
  assert to_int_list("100")==[100]
output: def to_int_list(s):
      return [int(x) for x in s.split(',')]