Function run_md_pump 

pub async fn run_md_pump(
    core: Arc<Mutex<MdCore>>,
    emitter: Arc<Emitter>,
    rx: AsyncReceiver<IncomingMessage>,
    cancel: CancellationToken,
)

Runs the market data event pump until cancel fires or the frame channel closes.

Every frame from rx goes through core and the resulting events to emitter. Events that a slow bot left in the subscription buffers are offered again every 20 ms.