fix(notify): 根治低带宽控制面阻塞与传输写入卡死

- 为控制消息增加优先级、公平调度、队列字节预算和自适应批处理
- 支持可取消的写门等待，收紧 shared/dedicated bulk、stream 和 Reply 写入边界
- 修复 bulk reset/close、连接 handoff 和安全 profile 切换时序
- 保留旧取消与超时错误契约，新增阶段化 TransportSendError
- 增加 ReplyCtx、ReplyObjCtx、写超时配置及黑洞连接和竞态回归测试

peer_error.go

@@ -63,6 +63,13 @@ func transportDetachedError(detail string, cause error) error {
 	return newDetailedStateError(errTransportDetached, detail, cause)
 }
 
+// IsTransportDetachedError reports whether err means that the physical
+// transport was detached. The result remains true through the detailed and
+// transport-send wrappers used by the public send/read APIs.
+func IsTransportDetachedError(err error) bool {
+	return err != nil && errors.Is(err, errTransportDetached)
+}
+
 func clientTransportDetachedError(c *ClientCommon) error {
 	if c == nil {
 		return errTransportDetached