Don't wait in the tesrver idle testing every time around the loop

If we wait for 100ms 600 times - then the test takes a minute to complete
which is far too long. The purpose of the wait is to give the assistance
thread a chance to catch up. We only do that if the event timeout has
actually expired - otherwise we are waiting for no reason.

Fixes #22156

Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from #22284)

test/quic_tserver_test.c

@@ -305,14 +305,26 @@ static int do_test(int use_thread_assist, int use_fake_time, int use_inject)
         if (c_start_idle_test && !c_done_idle_test) {
             /* This is more than our default idle timeout of 30s. */
             if (idle_units_done < 600) {
+                struct timeval tv;
+                int isinf;
+
                 if (!TEST_true(CRYPTO_THREAD_write_lock(fake_time_lock)))
                     goto err;
                 fake_time = ossl_time_add(fake_time, ossl_ms2time(100));
                 CRYPTO_THREAD_unlock(fake_time_lock);
 
                 ++idle_units_done;
                 ossl_quic_conn_force_assist_thread_wake(c_ssl);
-                OSSL_sleep(100); /* Ensure CPU scheduling for test purposes */
+
+                /*
+                 * If the event timeout has expired then give the assistance
+                 * thread a chance to catch up
+                 */
+                if (!TEST_true(SSL_get_event_timeout(c_ssl, &tv, &isinf)))
+                    goto err;
+                if (!isinf && ossl_time_compare(ossl_time_zero(),
+                                                ossl_time_from_timeval(tv)) >= 0)
+                    OSSL_sleep(100); /* Ensure CPU scheduling for test purposes */
             } else {
                 c_done_idle_test = 1;
             }