[3.12] gh-110666: Fix multiprocessing test_terminate() elapsed (GH-110667) (#110668)

gh-110666: Fix multiprocessing test_terminate() elapsed (GH-110667)

multiprocessing test_terminate() and test_wait_socket_slow() no
longer test the CI performance: no longer check maximum elapsed time.

Add CLOCK_RES constant: tolerate a difference of 100 ms.
(cherry picked from commit 1556f426da3f2fb5842689999933c8038b65c034)

Co-authored-by: Victor Stinner <vstinner@python.org>