input: Write a function to reverse a given list of integers. The function should return the list with its elements in reverse order.
  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([7,8,9,1,2,3])==[3,2,1,9,8,7]
  assert reverse_list([])==[]
  assert reverse_list([1])==[1]
output: def reverse_list(lst):
      return lst[::-1]