system/qtest: properly feedback results of clock_[step|set]

system/qtest: properly feedback results of clock_[step|set]

Time will not advance if the system is paused or there are no timer
events set for the future. In absence of pending timer events
advancing time would make no difference the system state. Attempting
to do so would be a bug and the test or device under test would need
fixing.

Tighten up the result reporting to `FAIL` if time was not advanced.

Reviewed-by: Fabiano Rosas <farosas@suse.de>
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2687
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20250108121054.1126164-18-alex.bennee@linaro.org>