Create isValidURN and isValidURI and use isValidURI everywhere where it is needed

outOfLineContent.go

@@ -22,7 +22,7 @@ func newOutOfLineContent(mediaType string, content any) (*OutOfLineContent, erro
 		return nil, fmt.Errorf("content type %T incompatible with out of line content", content)
 	}
 
-	if !isValidURL(content.(URI)) {
+	if !isValidURI(content.(URI)) {
 		return nil, errors.New("content not a valid uri")
 	}