Function close_implies_flush

pub async fn close_implies_flush<A, B, S, E>(alice: A, bob: B)
where
    A: StreamMuxer<Substream = S, Error = E> + Unpin,
    B: StreamMuxer<Substream = S, Error = E> + Unpin,
    S: AsyncRead + AsyncWrite + Send + Unpin + 'static,
    E: Debug,

Verifies that Alice can send a message and immediately close the stream afterwards and Bob can use read_to_end to read the entire message.