WT-12816 suggested a timeout for prefetch threads so they don't get stuck in eviction. The way it is correctly implemented can be confusing for the readers as we are in fact not using a timeout, we are relying on the timeout code and the timeout fires as soon as the prefetch flag is set on a session.
We can do it different by simply exiting the eviction loop if the same flag is set and leave the timeout code untouched.