#16699.

The changes are primarily in anacrolix/torrent, https://github.com/anacrolix/torrent/compare/d922d78d2e6135477b120daae537bf79a675d2c6..client-trackers.

Instead of firing off announces whenever we can, and maintaining a goroutine for every tracker and torrent combination, there's a dispatcher that reuses tracker announce clients, limits parallelism, and prioritizes announces to torrents that need them most, including doing things like avoiding announcing the same torrent to different trackers simultaneously unless there's nothing else to do, sending stop and completion events even when torrents are dropped, and avoiding announcing for torrents that have active webseed requests.

The impact for Erigon is that peers become available much sooner to the torrents that need them. Subjectively it goes from taking 5 mins or more to ~5-10s to start downloading from peers. There's also a possible issue around webseeds stalling if peers weren't present to tickle certain states that was fixed. I also added a hard webseed request stall fix after encountering it more often now that peers were more active on non-webseeding torrents.

There's a few optimizations that might be available down the road. The new indexing uses values instead of references in a lot of places, a careful strategy but probably results in a lot more cache and memory use than really necessary. It shouldn't show up in profiling as very large, but if it does there's plenty of easy stuff to improve once the concept has proven itself.

There's also a bunch of logging fixes in varous places. I expect to see a panic or two for edge cases I missed. There was a nagging one around some state not being propagated correctly but I think I've resolved that now.