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Withe queries (particularly providers), it was possible to
exit the query runner's Run BEFORE all its children were done,
because the runner itself only listened to the context. This
introduced the possibility of a panic (you can go check it
out by running the TestProvidersMany test on dht_test in commits
before this one).  Thankfully, ctxgroup saved the day with
almost _zero_ changes to the sync flow, and now we have the
guarantee that the query runner will only exit if all its
children are done. ❤

Conflicts:
	routing/dht/query.go

this is a major refactor of the entire codebase
it changes the monolithic peer.Peer into using
a peer.ID and a peer.Peerstore.

Other changes:
- removed handshake3.
-	testutil vastly simplified peer
-	secio bugfix + debugging logs
-	testutil: RandKeyPair
-	backpressure bugfix: w.o.w.
-	peer: added hex enc/dec
-	peer: added a PeerInfo struct
  PeerInfo is a small struct used to pass around a peer with
 	a set of addresses and keys. This is not meant to be a
 	complete view of the system, but rather to model updates to
 	the peerstore. It is used by things like the routing system.
-	updated peer/queue + peerset
-	latency metrics
-	testutil: use crand for PeerID gen
 	RandPeerID generates random "valid" peer IDs. it does not
 	NEED to generate keys because it is as if we lost the key
 	right away. fine to read some randomness and hash it. to
 	generate proper keys and an ID, use:
 	  sk, pk, _ := testutil.RandKeyPair()
 	  id, _ := peer.IDFromPublicKey(pk)
 	Also added RandPeerIDFatal helper
- removed old spipe
- updated seccat
- core: cleanup initIdentity
- removed old getFromPeerList