fix: write操作在batchBuffer为nil时也触发重连

- 解决"假连接"边界情况：状态为connected但batchBuffer为nil
- 确保发送消息失败后能自动恢复连接

Sources/Nats/NatsConnection.swift

@@ -1056,6 +1056,13 @@ class ConnectionHandler: ChannelInboundHandler {
 
     func write(operation: ClientOp) async throws {
         guard let buffer = self.batchBuffer else {
+            // If state is connected but batchBuffer is nil, this is a "fake connection" state
+            // Trigger reconnect to recover
+            let currentState = state.withLockedValue { $0 }
+            if currentState == .connected {
+                logger.error("Write failed: batchBuffer is nil but state is connected, triggering reconnect")
+                handleDisconnect()
+            }
             throw NatsError.ClientError.invalidConnection("not connected")
         }
         do {