DEBUG: thread: make lock time computation more consistent

DEBUG: thread: make lock time computation more consistent

The lock time computation was a bit inconsistent between functions,
particularly those using a try_lock. Some of them would count the lock
as taken without counting the time, others would simply not count it.
This is essentially due to the way the time is retrieved, as it was
done inside the atomic increment.

Let's instead always use start_time to carry the elapsed time, by
presetting it to the negative time before the event and addinf the
positive time after, so that it finally contains the duration. Then
depending on the try lock's success, we add the result or not. This
was generalized to all lock functions for consistency, and because
this will be handy for future changes.