input: Write a python function to generate unique integers within a given range.
  assert list(unique_integers_generator(10, 20)) == [10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]
  assert list(unique_integers_generator(15, 18)) == [15, 16, 17, 18]
  assert list(unique_integers_generator(5, 5)) == [5]
output: def unique_integers_generator(start, end):
      for num in range(start, end + 1):
          yield num