Campbell Barton
e125305af4
Callbacks used in `bpy.props` didn't hold a references to the functions they used. While this has been the case since early 2.5x it didn't cause any problems as long as the class held a reference. With Python 3.10 or when using `from __future__ import annotations`, the annotations are no longer owned by the class once evaluated. Resolve this by holding a reference in the module, which now supports traverse & clear callbacks so the objects are visible to Python's garbage collector. Also refactor storage of Python data, moving from an array into a struct.