feat: error for when there is more source code than parsed

pkg/iterator/iterator.go

@@ -39,6 +39,15 @@ func (i Iterator[T]) Get() (T, error) {
 	return i.items[i.index], nil
 }
 
+func (i Iterator[T]) MustGet() T {
+	var null T
+	if i.Done() {
+		return null
+	}
+
+	return i.items[i.index]
+}
+
 // Create a new iterator, over a set of items.
 func (i *Iterator[T]) Next() (T, error) {
 	item, err := i.Get()