feat(notify): 重构通信内核并补齐 stream/bulk/record/transfer 能力

- 引入 LogicalConn/TransportConn 分层，ClientConn 保留兼容适配层
  - 新增 Stream、Bulk、RecordStream 三条数据面能力及对应控制路径
  - 完成 transfer/file 传输内核与状态快照、诊断能力
  - 补齐 reconnect、inbound dispatcher、modern psk 等基础模块
  - 增加大规模回归、并发与基准测试覆盖
  - 更新依赖库

send_state.go

@@ -0,0 +1,41 @@
+package notify
+
+import "errors"
+
+var (
+	errServiceShutdown   = errors.New("service shutdown")
+	errTransportDetached = errors.New("transport detached")
+)
+
+func (c *ClientCommon) ensureClientSendReady() error {
+	if !sessionIsAlive(&c.alive) {
+		return errServiceShutdown
+	}
+	if !c.clientTransportAttachedSnapshot() {
+		return clientTransportDetachedError(c)
+	}
+	return nil
+}
+
+func (s *ServerCommon) ensureServerSendReady(client *ClientConn) error {
+	if client == nil {
+		return s.ensureServerTransportSendReady(nil)
+	}
+	return s.ensureServerTransportSendReady(s.resolveOutboundTransport(logicalConnFromClient(client)))
+}
+
+func (s *ServerCommon) ensureServerTransportSendReady(transport *TransportConn) error {
+	if !sessionIsAlive(&s.alive) {
+		return errServiceShutdown
+	}
+	if s.serverUDPListenerSnapshot() != nil {
+		if transport == nil || transport.RemoteAddr() == nil || !transport.IsCurrent() {
+			return transportDetachedErrorForTransport(transport)
+		}
+		return nil
+	}
+	if transport == nil || !transport.Attached() || !transport.HasRuntimeConn() || !transport.IsCurrent() {
+		return transportDetachedErrorForTransport(transport)
+	}
+	return nil
+}