multi: add models.Node V1 constructor

Add a version field to models.Node and a V1 constructor for it.

graph/db/interfaces.go

@@ -111,7 +111,7 @@ type V1Store interface { //nolint:interfacebloat
 	// by two nodes to quickly determine if they have the same set of up to
 	// date node announcements.
 	NodeUpdatesInHorizon(startTime, endTime time.Time,
-		opts ...IteratorOption) iter.Seq2[models.Node, error]
+		opts ...IteratorOption) iter.Seq2[*models.Node, error]
 
 	// FetchNode attempts to look up a target node by its identity
 	// public key. If the node isn't found in the database, then