* Failing test: Expiring a partially completed tree
We should not throw out a partially completed tree if it expires in the
middle of rendering. We should finish the rest of the tree without
yielding, then finish any remaining expired levels in a single batch.
* Check if there's a partial tree before restarting
If a partial render expires, we should stay in the concurrent path
(performConcurrentWorkOnRoot); we'll stop yielding, but the rest of the
behavior remains the same.
We will only revert to the sync path (performSyncWorkOnRoot) when
starting on a new level.
This approach prevents partially completed concurrent work from
being discarded.
* New test: retry after error during expired render