This attempts to resolve upload conflicts by implementing cancel/cleanup on failed
uploads
* fix panic error on defer cancel upload
* increase pacer min sleep from 10 to 100 ms
* stop using uploadByForm()
* introduce force sleep before and after async tasks
* use pacer's retry scheme instead of manual implementation
Fixes#7787
Previously, `getFile()` was called indiscriminately during uploads, moves,
and download link generation. This could lead to users with download limit
causing subsequent operations like uploads and moves to fail.
This PR optimizes the use of getFile(), by only calling it
when it's strictly necessary.
Before this change, the Pikpak backend would always download
the first media item whenever possible, regardless of whether
or not it was the original contents.
Now we check the validity of a media link using the `fid`
parameter in the link URL.
Fixes#6992
