执行器回调日志落盘方案复用RPC序列化方案，并移除Jackson依赖；

xxl-job-core/src/main/java/com/xxl/job/core/thread/TriggerCallbackThread.java

 
     // ---------------------- fail-callback file ----------------------
 
-    private static String failCallbackFilePath = XxlJobFileAppender.getLogPath().concat(File.separator);
+    private static String failCallbackFilePath = XxlJobFileAppender.getLogPath().concat(File.separator).concat("callbacklog");
     private static String failCallbackFileName = failCallbackFilePath.concat("xxl-job-callback-{x}").concat(".log");
 
     private void appendFailCallbackFile(List<HandleCallbackParam> callbackParamList){