We-worked model to remove resolver.

lookups are performed inline now. keeps things simpler, however it has a performance knock, so it's time to refine async building were possible.

datamodel/low/3.0/external_doc.go

@@ -2,6 +2,7 @@ package v3
 
 import (
 	"github.com/pb33f/libopenapi/datamodel/low"
+	"github.com/pb33f/libopenapi/index"
 	"gopkg.in/yaml.v3"
 )
 
@@ -11,12 +12,7 @@ type ExternalDoc struct {
 	Extensions  map[low.KeyReference[string]]low.ValueReference[any]
 }
 
-func (ex *ExternalDoc) Build(root *yaml.Node) error {
-	// extract extensions
-	extensionMap, err := ExtractExtensions(root)
-	if err != nil {
-		return err
-	}
-	ex.Extensions = extensionMap
+func (ex *ExternalDoc) Build(root *yaml.Node, idx *index.SpecIndex) error {
+	ex.Extensions = ExtractExtensions(root)
 	return nil
 }