Improve accuracy of Task.withTimeout()

Currently the timeout action is executed as a timer task with the highest priority. It means that there is some delay between timer triggering and action being executed. In extreme cases the delay can be significant.
This task is to investigate different approach of executing timeouts that does not involve scheduling task and a plan's queue.

Start from Task.withTimeout() and trace how the timeout action is scheduled as a high-priority timer task and enters a plan's queue. Compare alternative timeout execution approaches, then document a concrete plan that avoids the stated scheduling delay and queue involvement.

Written by the indexing model from the issue text.