Restore teardown_websocket methods

These were mistakenly removed when basing Quart on Flask.

src/quart/app.py

@@ -955,6 +955,26 @@ async def func(response):
         self.after_websocket_funcs[None].append(func)
         return func
 
+    @setupmethod
+    def teardown_websocket(
+        self,
+        func: T_teardown,
+    ) -> T_teardown:
+        """Add a teardown websocket function.
+        This is designed to be used as a decorator, if used to
+        decorate a synchronous function, the function will be wrapped
+        in :func:`~quart.utils.run_sync` and run in a thread executor
+        (with the wrapped function returned). An example usage,
+        .. code-block:: python
+            @app.teardown_websocket
+            async def func():
+                ...
+        Arguments:
+            func: The teardown websocket function itself.
+        """
+        self.teardown_websocket_funcs[None].append(func)
+        return func
+
     async def handle_http_exception(
         self, error: HTTPException
     ) -> HTTPException | ResponseReturnValue:

src/quart/blueprints.py

@@ -64,6 +64,9 @@ def __init__(self, *args: t.Any, **kwargs: t.Any) -> None:
         self.before_websocket_funcs: t.Dict[AppOrBlueprintKey, t.List[BeforeWebsocketCallable]] = (
             defaultdict(list)
         )
+        self.teardown_websocket_funcs: dict[AppOrBlueprintKey, list[TeardownCallable]] = (
+            defaultdict(list)
+        )
 
     def get_send_file_max_age(self, filename: str | None) -> int | None:
         """Used by :func:`send_file` to determine the ``max_age`` cache
@@ -263,6 +266,27 @@ async def func(response):
         self.after_websocket_funcs[None].append(func)
         return func
 
+    @setupmethod
+    def teardown_websocket(
+        self,
+        func: T_teardown,
+    ) -> T_teardown:
+        """Add a teardown websocket function.
+        This is designed to be used as a decorator, if used to
+        decorate a synchronous function, the function will be wrapped
+        in :func:`~quart.utils.run_sync` and run in a thread executor
+        (with the wrapped function returned). An example usage,
+        .. code-block:: python
+            @app.teardown_websocket
+            async def func():
+                ...
+        Arguments:
+            func: The teardown websocket function itself.
+            name: Optional blueprint key name.
+        """
+        self.teardown_websocket_funcs[None].append(func)
+        return func
+
     @setupmethod
     def before_app_websocket(self, func: T_before_websocket) -> T_before_websocket:
         """Add a before websocket to the App.