Change audio/video playback to stop playback when out of view

[Gargron]

• Change video player to not loop, since the audio player doesn't
• Change playback and mute buttons to feel snappier

[ClearlyClaire]

I personally would oppose to this for two main reasons:

• actually, I prefer media to keep playing when scrolling, especially when it's mostly audio and I'm in a thread view. I hate what Twitter does in that regard
• this would be inconsistent with media from preview cards, which we can't control… (well, we could unload them completely, but I'd find it even more annoying)

[Gargron]

The intersection observer or the reducer do unload the media when it's scrolled away, it's just not immediate. I feel like this way is cleaner, makes it a more consistent behaviour than "keep scrolling and at some point it'll just stop playback, or maybe not until new toots come in from top"