Fix failure checking on rcu_read_lock

Fix failure checking on rcu_read_lock

during memfail testing:
https://github.com/openssl/openssl/actions/runs/16794088536/job/47561223902

We get lots of test failures in ossl_rcu_read_lock.  This occurs
because we have a few cases in the read lock path that attempt mallocs,
which, if they fail, trigger an assert or a silent failure, which isn't
really appropriate.  We should instead fail gracefully, by informing the
caller that the lock failed, like we do for CRYPTO_THREAD_read_lock.

Fortunately, these are all internal apis, so we can convert
ossl_rcu_read_lock to return an int indicating success/failure, and fail
gracefully during the test, rather than hitting an assert abort.

Fixes openssl/project#1315

Reviewed-by: Paul Yang <paulyang.inf@gmail.com>
Reviewed-by: Dmitry Belyavskiy <beldmit@gmail.com>
Reviewed-by: Paul Dale <ppzgs1@gmail.com>
(Merged from https://github.com/openssl/openssl/pull/28195)