Fetcher improvements

[janos]

Fetchers are using singleflight to deduplicate retrieval of the same chunk. The consequence is that a relation between chunk requests is made, terminating later chunk requests sooner than the timeout is specified as the first requests that times out terminates all other.

Implement peers to skip on fetcher.

Remove LNetStore by getting the peer from the passed context value. Remove origin peer by providing it in peers to skip.

Re-request chunk if requested peer disconnects.

[acud]

Add retry after sync failure.

what does this mean?

[janos]

Yes, syncing is not relevant here, removed, thanks.