gh-94675: Add a regression test for rjsmin re slowdown (GH-94685)

Adds a regression test for an re slowdown observed by rjsmin.
Uses multiprocessing to kill the test after SHORT_TIMEOUT.

Co-authored-by: Oleg Iarygin <dralife@yandex.ru>
Co-authored-by: Christian Heimes <christian@python.org>