input: Write a function to create a copy of a list.
  assert copy_list([1, 2, 3, 4, 5]) == [1, 2, 3, 4, 5]
  assert copy_list(['a', 'b', 'c']) == ['a', 'b', 'c']
  assert copy_list([]) == []
output: def copy_list(lst):
      return lst[:]