Replace busy-wait spin_loop() in FenceTimeline::wait() with
Condvar::wait_timeout(). signal() now calls notify_all() to
wake blocked threads. This turns syncobj_wait from CPU-burning
poll to proper blocking sleep/wake.
Add two new tests:
- test_wait_wakes_on_signal: spawns a thread that signals
after 10ms, verifies the blocked wait wakes within 1s
- test_wait_timeout_expires: verifies 1ms timeout on an
unsignaled fence returns an error
vasilito
77c9fd5004