input: Write a function to generate a range of numbers using a generator function.
  assert list(num_range_generator(1, 5)) == [1, 2, 3, 4, 5]
  assert list(num_range_generator(3, 7)) == [3, 4, 5, 6, 7]
  assert list(num_range_generator(0, 0)) == [0]
output: def num_range_generator(start, end):
      for num in range(start, end + 1):
          yield num