CommentRepliesSource: Add cache for reply fetching

[Profpatsch]

There is no cache in the comment replies fetching, causing the app to reload them each time the device is rotated or a switch between the description content view tab and the comments one is done. This regression must be fixed.

Originally posted by @AudricV in #11060 (comment)

[SttApollo]

Can you assign this to me please?

[opusforlife2]

I've assigned you to another issue for now. It would be better to tackle things one at a time. Once you get used to what the devs expect in terms of code, you're welcome to take up further issues.