The transition to v2 will be incremental. To support that, we need
adaptors between v1 and v2 which will be inserted at places which are
boundaries of conversion.
The v1 -> v2 converter needs to accumulate range tombstones, so has unbounded worst case memory footprint.
The v2 -> v1 converter trims range tombstones around clustering rows,
so generates more fragments than necessary.
Because of that, adpators are a temporary solution and we should not
release with them on the produciton code paths.
