input: Write a function to reverse a list. Return the reversed list as output.
  assert reverse_list([1, 2, 3, 4, 5])==[5, 4, 3, 2, 1]
  assert reverse_list([10, 20, 30])==[30, 20, 10]
  assert reverse_list([])==[]
  assert reverse_list([1])==[1]
output: def reverse_list(lst):
      return lst[::-1]