Function pull_latest_ticker 

pub async fn pull_latest_ticker(
    backend: &BackendConn,
    stock_id: u64,
    nn_mkt_type: u8,
    common_session: i32,
    pull_count: u32,
    broker_id: Option<i32>,
) -> Result<TickRsp>

拉取最新逐笔，用于对齐 C++ Qot_Sub 成功后“订阅逐笔要提前拉一根”。

Ref:

• APIServer_Qot_Sub.cpp:265-280: subscribe Ticker 后调用 PullNewestTickerList_Lot(..., 1, false, SessionToNN(enSession)).
• NNBiz_Qot_PullQot.cpp:126-129: 非 US 强制 RTH，再从 latest key 拉取。
• NNBiz_Qot_PullQot.cpp:327-365: CMD6128 body + reserved[0]=head market, reserved[1]=NN_QuoteExType_SECURITY(0).