input: Write a function to get the length of strings in a list.
  assert length_strings(["apple", "banana", "mango"]) == [5, 6, 5]
  assert length_strings(["hello", "world"]) == [5, 5]
  assert length_strings(["a", "ab", "abc", "abcd"]) == [1, 2, 3, 4]
output: def length_strings(lst):
      return [len(s) for s in lst]