cmd/swarm/swarm-snapshot: swarm snapshot generator (#18453)

* cmd/swarm/swarm-snapshot: add binary to create network snapshots

* cmd/swarm/swarm-snapshot: refactor and extend tests

* p2p/simulations: remove unused triggerChecks func and fix linter

* internal/cmdtest: raise the timeout for killing TestCmd

* cmd/swarm/swarm-snapshot: add more comments and other minor adjustments

* cmd/swarm/swarm-snapshot: remove redundant check in createSnapshot

* cmd/swarm/swarm-snapshot: change comment wording

* p2p/simulations: revert Simulation.Run from master

https://github.com/ethersphere/go-ethereum/pull/1077/files#r247078904

* cmd/swarm/swarm-snapshot: address pr comments

* swarm/network/simulations/discovery: removed snapshot write to file

* cmd/swarm/swarm-snapshot, swarm/network/simulations: removed redundant connection event check, fixed lint error

swarm/network/kademlia.go

@@ -640,6 +640,8 @@ func (k *Kademlia) saturation() int {
 	})
 	// TODO evaluate whether this check cannot just as well be done within the eachbin
 	depth := depthForPot(k.conns, k.NeighbourhoodSize, k.base)
+
+	// if in the iterator above we iterated deeper than the neighbourhood depth - return depth
 	if depth < prev {
 		return depth
 	}