protocols: implement ext-foreign-toplevel-list-v1

clean up foreign toplevel destruction: don't `retain` to remove one item

document why we have duplicate destruction logic in foreign toplevel

messy to have two of the same comment but like how else do i make that
information readily available to both

Co-authored-by: HigherOrderLogic <73709188+HigherOrderLogic@users.noreply.github.com>

Author: 2 people