fix: 改进串口写入错误日志

1. 移除 write_command 中的 try-catch，让错误向上抛出
2. 在 write 方法中添加更详细的错误日志
3. 直接调用 _serial.write() 而不是先检查 is_connected

custom_components/sigmesh_gateway/serial_reader.py

@@ -292,10 +292,18 @@ class SerialReader:
 
     async def write(self, data: bytes) -> int:
         """写入数据到串口."""
-        if not self.is_connected:
+        _LOGGER.debug("write 方法：is_connected=%s, _serial=%s", self.is_connected, self._serial)
+        if self._serial is None:
+            _LOGGER.error("串口对象未初始化")
             raise RuntimeError("串口未连接")
 
-        return self._serial.write(data)  # type: ignore[union-attr]
+        try:
+            result = self._serial.write(data)
+            _LOGGER.debug("串口写入成功：%d 字节", result)
+            return result
+        except Exception as e:
+            _LOGGER.error("串口写入失败：%s (is_open=%s)", e, self._serial.is_open)
+            raise
 
     async def write_command(self, command: str) -> int:
         """写入 AT 命令."""