Add support for --mark-watched flag (like the one included in yt-dlp)

[NoExplorer]

Hello,

I've started to use your program, and although super useful, trying to calculate the size of playlists like your History page (:ythistory), it also counts duplicate videos, which wouldn't be downloaded because they would already exist (If I understood correctly that flag in yt-dlp, it should skip counting same links and move to the next one). That kind of throws off the estimated size, and I find the inclusion of support for the --mark-watched flag (as the one included in yt-dlp) would help a lot for people doing something like going about downloading playlists like these (:ythistory).

Hope I worded everything correctly.
That's all.