cache shortest path to network peers

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Because webrtc connections have significantly more overhead than UDP connections we use relayed message propagation instead of KAD traversal. Messages are suffixed with a host id and signature by each relaying peer...

• cache the next hop (the last relaying peer) corresponding to the shortest path to transitive peers
• query cache to inform routing decisions
• add timestamps to hop trailers to compute relative latency to peers
• use khh to filter popular service host ids and store multiple next hops
• estimate deliverability confidence to reduce message replication