feat: Add concurrency and headless options for downloads

This commit introduces new features for controlling the download process:

-   **Concurrency**: Users can now specify the number of concurrent volume downloads using the `--concurrency` flag. This significantly speeds up the download of entire novels.
-   **Headless Mode**: A `--headless` flag has been added to control whether the browser operates in headless mode (without a visible UI). This is useful for debugging or running in environments without a display.

**Changes include:**

-   Updated `download` command to accept `--concurrency` and `--headless` flags.
-   Refactored `bilinovel` downloader to support `BilinovelNewOption` for configuring headless mode and concurrency.
-   Implemented a page pool and concurrency control mechanism within the `bilinovel` downloader to manage concurrent browser page usage.
-   Added `DownloadNovel` and `DownloadVolume` methods to the `bilinovel` downloader, utilizing goroutines and wait groups for parallel processing.
-   Updated `.vscode/launch.json` with new configurations for testing novel and volume downloads with the new options.

downloader/downloader.go

@@ -0,0 +1,12 @@
+package downloader
+
+import "bilinovel-downloader/model"
+
+type Downloader interface {
+	GetNovel(novelId int, skipChapterContent bool, skipVolumes []int) (*model.Novel, error)
+	GetVolume(novelId int, volumeId int, skipChapterContent bool) (*model.Volume, error)
+	GetChapter(novelId int, volumeId int, chapterId int) (*model.Chapter, error)
+	GetStyleCSS() string
+	GetExtraFiles() []model.ExtraFile
+	Close() error
+}