feat(type): add nodebuilder hint to typed links

Add the concept of a suggested node builder to links that are a reference to a specific typed node
that has a code-gen'd node builder

impl/typed/typedLink.go

+package typed
+
+import "github.com/ipld/go-ipld-prime"
+
+// typed.Link is a superset of the ipld.Link interface, and has one additional behavior.
+//
+// A typed.Link contains a hint for the appropriate node builder to use for loading data
+// on the other side of a link, so that it can be assembled into a node representation
+// and validated against the schema as quickly as possible
+//
+// So, for example, if you wanted to support loading the other side of a link
+// with a code-gen'd node builder while utilizing the automatic loading facilities
+// of the traversal package, you could write a LinkNodeBuilderChooser as follows:
+//
+// func LinkNodeBuilderChooser(lnk ipld.Link, lnkCtx ipld.LinkContext) ipld.NodeBuilder {
+//  if tlnk, ok := lnk.(typed.Link); ok {
+//    return tlnk.SuggestedNodeBuilder()
+//  }
+//	return ipldfree.NodeBuilder()
+// }
+//
+type Link interface {
+	SuggestedNodeBuilder() ipld.NodeBuilder
+}

traversal/common.go

@@ -7,6 +7,7 @@ import (
 
 	ipld "github.com/ipld/go-ipld-prime"
 	ipldfree "github.com/ipld/go-ipld-prime/impl/free"
+	"github.com/ipld/go-ipld-prime/impl/typed"
 )
 
 // init sets all the values in TraveralConfig to reasonable defaults
@@ -21,7 +22,10 @@ func (tc *Config) init() {
 		}
 	}
 	if tc.LinkNodeBuilderChooser == nil {
-		tc.LinkNodeBuilderChooser = func(ipld.Link, ipld.LinkContext) ipld.NodeBuilder {
+		tc.LinkNodeBuilderChooser = func(lnk ipld.Link, lnkCtx ipld.LinkContext) ipld.NodeBuilder {
+			if tlnk, ok := lnk.(typed.Link); ok {
+				return tlnk.SuggestedNodeBuilder()
+			}
 			return ipldfree.NodeBuilder()
 		}
 	}