input: Write a python function to reverse an array.
  assert reverse_array([1, 2, 3, 4, 5]) == [5, 4, 3, 2, 1]
  assert reverse_array(['a', 'b', 'c', 'd']) == ['d', 'c', 'b', 'a']
  assert reverse_array([10, 20, 30, 40]) == [40, 30, 20, 10]
output: def reverse_array(arr):
      return arr[::-1]