input: Write a function named to_int_list that converts a given string of comma-separated numbers into a list of integers. The function should take a single parameter s which is the string to be converted.
  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("0,0,0")==[0, 0, 0]
  assert to_int_list("1,2,3,4,5,6")==[1, 2, 3, 4, 5, 6]
  assert to_int_list("2,4,6,8,10")==[2, 4, 6, 8, 10]
output: return [int(num) for num in s.split(',')]