Fix run loop slow task and priority accounting

Some extra work was [recently added](https://github.com/apple/foundationdb/pull/6252) to Net2's inner run loop. This work will interfere with the run loop slow task and priority tracking metrics, especially if this new work takes a long time (something that has been known to happen).

This new work should be tracked separately and accounted for as its own task and at the proper priority to avoid attributing it to an adjacent task.

Start with Net2's inner run loop and review the extra work introduced in PR 6252. Trace how the run-loop slow task and priority metrics account for that work. Done means the new work is tracked separately at its proper priority and is not attributed to an adjacent task.

Written by the indexing model from the issue text.