Own iterator geometry results

Return independent geometry copies with unique ownership, preserve parent lifetimes, and teach the Python wrapper to own derived results. Keep serializer inputs non-owning and replace Collada's deferred object with copied triangulation elements.\n\nGenerated with the assistance of an AI coding tool.

src/ifcconvert/validate_storey_containment.cpp

@@ -111,7 +111,7 @@ void fix_storeycontainment(ifcopenshell::file& f, bool no_progress, bool quiet,
 		if (num_created) {
 			has_more = context_iterator.next();
 		}
-		ifcopenshell::geom::brep_element* geom_object = nullptr;
+		std::unique_ptr<ifcopenshell::geom::brep_element> geom_object;
 		if (has_more) {
 			geom_object = context_iterator.get_native();
 		}