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