After the transition to the new in-memory representation in
aab6b0ee27 'Merge "Introduce new in-memory
representation for cells" from Paweł'
atomic_cell_or_collection::external_memory_usage() stopped accounting
for the externally stored data. Since, it wasn't covered by the unit
tests the bug remained unnotices until now.
This series fixes the memory usage calculation and adds proper unit
tests.
* https://github.com/pdziepak/scylla.git fix-external-memory-usage/v1:
tests/mutation: properly mark atomic_cells that are collection members
imr::utils::object: expose size overhead
data::cell: expose size overhead of external chunks
atomic_cell: add external chunks and overheads to
external_memory_usage()
tests/mutation: test external_memory_usage()
(cherry picked from commit 2ffb621271)