In several places in gossip code, the entire crds table is scanned only
to filter out nodes' contact infos. Currently on mainnet, crds table is
of size ~70k, while there are only ~470 nodes. So the full table scan is
inefficient. Instead we may maintain an index of only nodes' contact
infos.
Based on run-time profiles, the majority time of new_pull_requests is
spent building bloom filters, in hashing and bit-vec ops.
This commit builds crds filters in parallel using rayon constructs. The
added benchmark shows ~5x speedup (4-core machine, 8 threads).