[Feature] Offline Anime Viewing

[aiko-chan-ai]

I recently discovered this amazing app, thank you for developing it.
I would like to have an offline anime viewing feature for the app because while traveling, watching anime consumes a lot of mobile data. It would be similar to YouTube's feature.

[tachibana-shin]

I have implemented this function but have not enabled it. The app only provides high quality videos so each episode really takes up a lot of memory (600MB for 1 episode) does your device have enough space for it?

[FiorenMas]

I have implemented this function but have not enabled it. The app only provides high quality videos so each episode really takes up a lot of memory (600MB for 1 episode) does your device have enough space for it?

Is this pull request ready to be merged into the main branch? I really need this feature.