Function start_io_loop 

pub(super) fn start_io_loop<B, W, R, Wr>(
    client: &Arc<Client<B, W>>,
    reader: R,
    writer: Wr,
)
where
    B: JsonRpcCodec,
    W: WsCodec,
    R: MessageRx<Message = Value> + Send + 'static,
    Wr: MessageTx<Message = Value> + Send + 'static,

Spawn the reader/writer task that drives the multiplexed wire.