swarm/network: Keep span across roundtrip (#19140)

* swarm/newtork: WIP Span request span until delivery and put

* swarm/storage: Introduce new trace across single fetcher lifespan

* swarm/network: Put span ids for sendpriority in context value

* swarm: Add global span store in tracing

* swarm/tracing: Add context key constants

* swarm/tracing: Add comments

* swarm/storage: Remove redundant fix for filestore

* swarm/tracing: Elaborate constants comments

* swarm/network, swarm/storage, swarm:tracing: Minor cleanup

swarm/swarm.go

@@ -426,6 +426,7 @@ func (s *Swarm) Start(srv *p2p.Server) error {
 func (s *Swarm) Stop() error {
 	if s.tracerClose != nil {
 		err := s.tracerClose.Close()
+		tracing.FinishSpans()
 		if err != nil {
 			return err
 		}