Make file operations atomic

[wisp3rwind]

As discussed in beetbox/beets#3849 and beetbox/beets#4060, we would like most/all of beets file operations to be atomic. This requires support by mediafile, which in turn either requires that we shuffle around temporary files, or someone invests the time to implement this in mutagen directly, see quodlibet/mutagen#241. Ideally, on CoW file systems, this should use reflinks.

[catap]

@wisp3rwind this seems like a huge project for mutagen to be honest.

Anyway, usually it edits only end of a file which seems fast enough.

Anyway, embeded arts may easy make things slow :(

[wisp3rwind]

Sure, this might involve a lot of work and will depend on a volunteer to do so. I opened this issue to keep track of the problem, since the previous discussion is mostly in the review comments in beetbox/beets#4060 and as such hard to find.

[catap]

@wisp3rwind meanwhie, I'll try to find any motivation to implement a way with tempfiles also here ;)