input: Write a python function to generate a list of unique numbers from 0 to N.
  assert unique_numbers(10) == [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
  assert unique_numbers(5) == [0, 1, 2, 3, 4, 5]
  assert unique_numbers(0) == [0]
output: def unique_numbers(N):
      return list(range(N+1))