start moving attributes to custom ops instead of magical lexicals
move this stuff out of the pad

this is probably a good idea? maybe?
not sure why SAVEGENERICSV doesn't work here
handle attribute access in class methods
support attributes with FETCH_DATA hooks

fall back to magically calling fetch_data_in_slot_for or
store_data_in_slot_for when accessing attributes with FETCH_DATA hooks
installed
cleanups
move the invocant back to the pad

no reason for this to be a custom op, really
the slot needs to be mortalized
actually copy the svs here, don't just bump the refcount