# R2-04 — miot_client: sub_device_state / unsub_device_state

## 缺失方法

Python `MIoTClient` 提供设备状态订阅：

```python
def sub_device_state(self, did: str, handler: Callable, handler_ctx: Any = None) -> bool
def unsub_device_state(self, did: str) -> bool
```

功能：订阅指定 did 的设备在线/离线状态变化通知。

## 目标文件

`D:\miot\go-miot\miot_client.go` 或 `miot_client_sub.go`

添加：
```go
func (c *MIoTClient) SubDeviceState(did string, handler func(string, MIoTDeviceState, interface{})) error
func (c *MIoTClient) UnsubDeviceState(did string) error
```