"whitelisting" mechanism (list of files - stored in DB) - which
protecting us from downloading new files after upgrade/downgrade was
broken. And seems it became over-complicated with time.
I replacing it by 1 persistent flag inside downloader:
"prohibit_new_downloads.lock"
Erigon will turn downloader into this mode after
downloading/verification of first snapshots.
```
//Corner cases:
// - Erigon generated file X with hash H1. User upgraded Erigon. New version has preverified file X with hash H2. Must ignore H2 (don't send to Downloader)
// - Erigon "download once": means restart/upgrade/downgrade must not download files (and will be fast)
// - After "download once" - Erigon will produce and seed new files
```
------
`downloader --seedbox` is never "prohibit new downloads"
Closes#8078
This change is primarily intended to support go 1.21, but as a
side-effect requires updating libp2p, which in turn triggers an update
of golang.org/x/exp which creates quite a bit of (simple) churn in the
slice sorting.
This change introduces a new `cmp.Compare` function which can be used to
return an integer satisfying the compare interface for slice sorting.
In order to continue to support mplex for libp2p, the change references
github.com/libp2p/go-libp2p-mplex instead. Please see the PR at
https://github.com/libp2p/go-libp2p/pull/2498 for the official usptream
comment that indicates official support for mplex being moved to this
location.
Co-authored-by: Jason Yellick <jason@enya.ai>
