input: Write a function to reverse an array in place.
  assert reverse_in_place([1, 2, 3, 4, 5, 6]) == [6, 5, 4, 3, 2, 1]
  assert reverse_in_place([10, 20, 30, 40]) == [40, 30, 20, 10]
  assert reverse_in_place([7, 8, 9]) == [9, 8, 7]
output: def reverse_in_place(arr):
      left, right = 0, len(arr) - 1
      while left < right:
          arr[left], arr[right] = arr[right], arr[left]
          left += 1
          right -= 1
      return arr