feat: add pikpak offline download function (#6648)

* add pikpak offline download function

* 完善PikPak离线下载功能

* 删除多余的代码

* add task cache to avoid too many requests about API

* 优化Status函数

* 完善所有功能,目前测试无BUG

* 减少缓存时间，优化添加离线任务的参数

internal/offline_download/all.go

@@ -3,5 +3,6 @@ package offline_download
 import (
 	_ "github.com/alist-org/alist/v3/internal/offline_download/aria2"
 	_ "github.com/alist-org/alist/v3/internal/offline_download/http"
+	_ "github.com/alist-org/alist/v3/internal/offline_download/pikpak"
 	_ "github.com/alist-org/alist/v3/internal/offline_download/qbit"
 )