feat: 优化为批量更新结果类的 toString 方法实现

- 为BatchUpdateErrorInfo类实现toString方法
- 重构BatchUpdateResult类的toString方法，调整字段顺序

src/main/java/xyz/zhouxy/jdbc/BatchUpdateErrorInfo.java

@@ -78,4 +78,17 @@ public class BatchUpdateErrorInfo {
         return errorType;
     }
 
+    /**
+     * 返回该错误信息的字符串表示，包含批次索引、错误类型和错误消息。
+     *
+     * @return 格式为 {@code "BatchUpdateErrorInfo{batchIndex=..., errorType=..., message=...}"} 的字符串
+     */
+    @Override
+    public String toString() {
+        return "BatchUpdateErrorInfo{"
+                + "batchIndex=" + batchIndex
+                + ", errorType=" + errorType.getName()
+                + ", message=" + cause.getMessage()
+                + "}";
+    }
 }

src/main/java/xyz/zhouxy/jdbc/BatchUpdateResult.java

@@ -230,10 +230,10 @@ public class BatchUpdateResult {
     @Override
     public String toString() {
         return "BatchUpdateResult ["
-                + "total=" + total
+                + "status=" + status
-                + ", batchCount=" + batchCount
+                + ", total=" + total
                 + ", batchSize=" + batchSize
-                + ", status=" + status
+                + ", batchCount=" + batchCount
                 + ", completeBatchCount=" + completeBatchCount
                 + ", successBatchCount=" + successBatchCount
                 + ", errorBatchCount=" + getErrorBatchCount()