fix: reject pending async deriveds on discard (#18308)

The rejects all async deriveds of a batch as `OBSOLETE`, so they don't
hang around and bail early without triggering the batch.

If we don't do this, an async derived can trigger the already done
batch, which schedules an effect that is never flushed. Because it is
never flushed the branches it touched on its way up are never cleared,
and so anything else in that subtree is now unreactive.