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/ifcgeom/tree.cpp

@@ -151,7 +151,8 @@ void ifcopenshell::geom::tree::add_file(ifcopenshell::geom::iterator& iterator)
 	}
 
 	do {
-		add_element(iterator.get());
+		auto element = iterator.get();
+		add_element(element.get());
 	} while (iterator.next());
 }