The query result writer now counts tombstones and cuts the page (marking
it as a short one) when the tombstone limit is reached. This is to avoid
timing out on large span of tombstones, especially prefixes.
In the case of unpaged queries, we fail the read instead, similarly to
how we do with max result size.
If the limit is 0, the previous behaviour is used: tombstones are not
taken into consideration at all.
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