fix aiohttp disconnect error on websockets

aiohttp will throw if the handler doesn't return anything.

```python
14:11:35 aiohttp ERRO Missing return statement on request handler
Traceback (most recent call last):
  File "/Users/steve/conda/envs/port/lib/python3.12/site-packages/aiohttp/web_protocol.py", line 653, in finish_response
    prepare_meth = resp.prepare
                   ^^^^^^^^^^^^
AttributeError: 'NoneType' object has no attribute 'prepare'
```

https://docs.aiohttp.org/en/stable/web_quickstart.html#websockets

rust/perspective-python/perspective/handlers/aiohttp.py

@@ -39,7 +39,7 @@ def __init__(self, **kwargs):
         self._request = kwargs.pop("request")
         super().__init__(**kwargs)
 
-    async def run(self) -> None:
+    async def run(self) -> web.WebSocketResponse:
         def inner(msg):
             asyncio.get_running_loop().create_task(self._ws.send_bytes(msg))
 
@@ -53,3 +53,4 @@ def inner(msg):
 
         finally:
             self.session.close()
+        return self._ws