Update `WebSocketProxy.__call__` to use `asyncio.TaskGroup`

[DontPanicO]

Feature or Enhancement

Move from asyncio.gather to asyncio.TaskGroup in WebSocketProxy.__call__.

Pitch

asyncio.TaskGroup (only available wih Python >= 3.11) has a more structured cancellation logic and (as stated from python docs) it should be preferred over asyncio.gather when there are no reasons to use one of the two over the other.

• Important: this will require for the next release to drop support for Python < 3.11

Actually, the implementation is:

async def _forward(
    client: WebSocket, target: websockets.WebSocketClientProtocol
) -> None:
    ...

async def _reverse(
    client: WebSocket, target: websockets.WebSocketClientProtocol
) -> None:
    ...

class WebSocketProxy:
    ...

    async def __call__(self) -> None:
        async with websockets.connect(self._server_endpoint) as target:
            self._forward_task = asyncio.create_task(
                _forward(self._client, target)
            )
            self._reverse_task = asyncio.create_task(
                _reverse(self._client, target)
            )
            await asyncio.gather(self._forward_task, self._reverse_task)

With asyncio.TaskGroup it'd be like:

...

    async def __call__(self) -> None:
        async with asyncio.TaskGroup() as tg:
            async with websockets.connect(self._server_endpoint) as target:
                self._forward_task = tg.create_task(
                    _forward(self._client, target)
                )
                self._reverse_task = tg.create_task(
                    _reverse(self._client, target)
                )

Entering websockets.connect in the taskgroup context ensures that if any failure with target occurs, our child tasks (and the partent too) would properly cancel.