`AsyncIoStream` method `wait_closed()` raises attribute error

[mwilliamson-fourier]

When using AsyncIoStream, I've tried to use wait_closed() after closing the connection. However, doing so results in an error since it seems like a non-existent attribute is being referenced:

  File "/tmp/a/capnp-async-connection.py", line 12, in main
    await connection.wait_closed()
  File "capnp/lib/capnp.pyx", line 2414, in wait_closed
AttributeError: 'capnp.lib.capnp._PyAsyncIoStreamProtocol' object has no attribute 'closed_future'

The below should be a fairly minimal reproduction of the issue, assuming there's a server running on the relevant hostname and port:

import asyncio

import capnp

async def main():
    async with capnp.kj_loop():
        connection = await capnp.AsyncIoStream.create_connection(
            host="127.0.0.1",
            port=8000,
        )

        connection.close()
        await connection.wait_closed()


asyncio.run(main())

Am I using wait_closed() incorrectly, or is this a bug in pycapnp?