Fix retrieval tests and simulation backends (#17723)

* swarm/network/stream: introduced visualized snapshot sync test

* swarm/network/stream: non-existing hash visualization sim

* swarm/network/stream: fixed retrieval tests; new backend for visualization

* swarm/network/stream: cleanup of visualized_snapshot_sync_sim_test.go

* swarm/network/stream: rebased PR on master

* swarm/network/stream: fixed loop logic in retrieval tests

* swarm/network/stream: fixed iterations for snapshot tests

* swarm/network/stream: address PR comments

* swarm/network/stream: addressed PR comments

p2p/simulations/events.go

@@ -58,6 +58,9 @@ type Event struct {
 
 	// Msg is set if the type is EventTypeMsg
 	Msg *Msg `json:"msg,omitempty"`
+
+	//Optionally provide data (currently for simulation frontends only)
+	Data interface{} `json:"data"`
 }
 
 // NewEvent creates a new event for the given object which should be either a