input: Write a function to convert a given string to a list of integers. The string is expected to be a comma-separated sequence of numbers.
  assert to_int_list("1,2,3,4,5")==[1, 2, 3, 4, 5]
  assert to_int_list("10,20,30,40,50")==[10, 20, 30, 40, 50]
  assert to_int_list("5,15,25,35,45")==[5, 15, 25, 35, 45]
  assert to_int_list("")==[]
  assert to_int_list("1")==[1]
output: def to_int_list(s):
      return [int(x) for x in s.split(',') if x]