feat(thunder): add offline download tool (#7673)

* feat(thunder): add offline download tool

* fix(thunder): improve error handling and parse file size in status response

---------

Co-authored-by: Andy Hsu <i@nn.ci>

internal/offline_download/tool/add.go

@@ -77,6 +77,10 @@ func AddURL(ctx context.Context, args *AddURLArgs) (task.TaskExtensionInfo, erro
 		tempDir = args.DstDirPath
 		// 防止将下载好的文件删除
 		deletePolicy = DeleteNever
+	case "thunder":
+		tempDir = args.DstDirPath
+		// 防止将下载好的文件删除
+		deletePolicy = DeleteNever
 	}
 
 	taskCreator, _ := ctx.Value("user").(*model.User) // taskCreator is nil when convert failed