fix compatibility with pytest 8.2 by restoring deleted finalizers

[jakkdl]

Fixes #267

The problem in #267 arose from pytest-dev/pytest#11833, which made pytest not add finalizers for cached fixtures.
pytest_runtest_teardown relied on cached fixtures getting their finalizers repeatedly re-added, as it deleted all(?) finalizers on every re-run. This PR makes sure to save away those finalizers, so we can add them back when we're done rerunning and let them execute.

I suspect the current solution will break with xdist or something, given that suspended_finalizers is a global dict. So it'd probably be more prudent to do something with the database?

This is my first time looking at pytest-rerunfailures, so I'd love if any current maintainers wanted to have opinions or even finish up the PR now that I've mostly figured out the messy part.

[icemac]

I like the change. As it fixes our tests it is definitly a step forward.

[icemac]

Thank you very much for digging into this issue.

[icemac]

Hm, this seems to have fixed the problems for 8.3, when running explicitly against 8.2 there are still failures, see https://github.com/pytest-dev/pytest-rerunfailures/actions/runs/11687465600/job/32545646408?pr=279 as an example.