fix: 改为静态方法, isError和isSuccess方法会被json序列化

isError和isSuccess会被json序列化
`{"error":false,"success":true}`

Signed-off-by: runphp <runphp@qq.com>

ruoyi-common/ruoyi-common-core/src/main/java/com/ruoyi/common/core/domain/R.java

@@ -103,13 +103,13 @@ public class R<T> implements Serializable
         this.data = data;
     }
 
-    public Boolean isError()
+    public static <T> Boolean isError(R<T> ret)
     {
-        return !isSuccess();
+        return !isSuccess(ret);
     }
 
-    public Boolean isSuccess()
+    public static <T> Boolean isSuccess(R<T> ret)
     {
-        return R.SUCCESS == getCode();
+        return R.SUCCESS == ret.getCode();
     }
 }