input: def insertion_sort(arr: List[int]) -> List[int]:
      """
      Sorts a given list of integers using the insertion sort algorithm.
      >>> insertion_sort([4, 2, 1, 3])
      [1, 2, 3, 4]
      >>> insertion_sort([1, 1, 1, 1])
      [1, 1, 1, 1]
      """
output:     for i in range(1, len(arr)):
          key = arr[i]
          j = i - 1
          while j >= 0 and key < arr[j]:
              arr[j + 1] = arr[j]
              j -= 1
          arr[j + 1] = key
      return arr