chore: 清理未使用的 Jackson ObjectMapper，调整测试可见性

- MqttFaultConsumerTest: 删除未使用的 ObjectMapper 实例和导入
- MqttFaultConsumer: insertTdEngine/triggermethod 改为 package-private
  以支持同包测试访问

iot-platform/src/main/java/com/iot/platform/mqtt/MqttFaultConsumer.java

@@ -103,7 +103,7 @@ public class MqttFaultConsumer extends AbstractMqttConsumer {
         });
     }
 
-    private void insertTdEngine(Map<String, Object> data, String topic) throws SQLException {
+    void insertTdEngine(Map<String, Object> data, String topic) throws SQLException {
 
         String[] topicParts = topic.split("/");
         if (topicParts.length < 2) {
@@ -127,7 +127,7 @@ public class MqttFaultConsumer extends AbstractMqttConsumer {
         tdEngineAlarm.recordFailure(newMap, controllerName, table);
     }
 
-    private void triggermethod(String topic, SysFault weather) {
+    void triggermethod(String topic, SysFault weather) {
 
         String deviceId = weather.getDevice_id();
         String type = weather.getType();

iot-platform/src/test/java/com/iot/platform/mqtt/MqttFaultConsumerTest.java

@@ -1,6 +1,5 @@
 package com.iot.platform.mqtt;
 
-import com.fasterxml.jackson.databind.ObjectMapper;
 import com.iot.platform.common.utils.NumericIdGenerator;
 import com.iot.platform.config.IotProperties;
 import com.iot.platform.domain.SysDevice;
@@ -66,8 +65,6 @@ class MqttFaultConsumerTest {
 
     private MqttFaultConsumer mqttFaultConsumer;
 
-    private final ObjectMapper objectMapper = new ObjectMapper();
-
     @BeforeEach
     void setUp() {
         mqttFaultConsumer = new MqttFaultConsumer(