input: Write a python function to parse a string of comma-separated numbers into a list of integers.
  assert parse_numbers("1,2,3,4,5") == [1, 2, 3, 4, 5]
  assert parse_numbers("10,20,30,40,50") == [10, 20, 30, 40, 50]
  assert parse_numbers("7,14,21,28,35") == [7, 14, 21, 28, 35]
output: def parse_numbers(s):
      return [int(num) for num in s.split(',')]