framework: Clean up task manager on close_framework()

This prevents crashes due to the tasks it spawns continuing to run

Backport of a32030d46e6a96547fe4ebe6b1036be652ef659f

panda/src/framework/pandaFramework.cxx

@@ -189,6 +189,8 @@ close_framework() {
 
   _event_handler.remove_all_hooks();
 
+  _task_mgr.cleanup();
+
   _is_open = false;
   _made_default_pipe = false;
   _default_pipe.clear();