sorts: make shell_sort work with any Comparable, not just int

Use a Comparable Protocol + TypeVar bound so that shell_sort
correctly expresses it can sort any orderable type, not just
integers. Adds string and float doctest examples.

Part of #15234

Author: Pradhyut21

sorts/shell_sort.py

@@ -2,28 +2,46 @@
 https://en.wikipedia.org/wiki/Shellsort#Pseudocode
 """
 
+from typing import Any, Protocol, TypeVar
+
+
+class Comparable(Protocol):
+    def __lt__(self, other: Any, /) -> bool: ...
+
+
+T = TypeVar("T", bound=Comparable)
+
+
+def shell_sort(collection: list[T]) -> list[T]:
+    """Pure implementation of shell sort algorithm in Python.
 
-def shell_sort(collection: list[int]) -> list[int]:
-    """Pure implementation of shell sort algorithm in Python
     :param collection:  Some mutable ordered collection with heterogeneous
     comparable items inside
     :return:  the same collection ordered by ascending
 
+    Examples:
     >>> shell_sort([0, 5, 3, 2, 2])
     [0, 2, 2, 3, 5]
     >>> shell_sort([])
     []
     >>> shell_sort([-2, -5, -45])
     [-45, -5, -2]
+    >>> shell_sort(["c", "a", "b"])
+    ['a', 'b', 'c']
+    >>> shell_sort([2.5, -1.0, 0.0])
+    [-1.0, 0.0, 2.5]
+    >>> shell_sort([0, 5, 3, 2, 2]) == sorted([0, 5, 3, 2, 2])
+    True
+    >>> shell_sort(["c", "a", "b"]) == sorted(["c", "a", "b"])
+    True
     """
     # Marcin Ciura's gap sequence
-
     gaps = [701, 301, 132, 57, 23, 10, 4, 1]
     for gap in gaps:
         for i in range(gap, len(collection)):
             insert_value = collection[i]
             j = i
-            while j >= gap and collection[j - gap] > insert_value:
+            while j >= gap and insert_value < collection[j - gap]:
                 collection[j] = collection[j - gap]
                 j -= gap
             if j != i: