Treatment of missing neighbours
In cubing_next_round, a missing neighbouring cell is currently treated with an if-break. Yet, it would seems sufficient to just ignore that missing cell. The break might imply that other neighbouring cells might not be cubulated, as the break stops the loop over the neighbouring cells.
This might be inconsequential in practice, but should be looked into and tested.
Current code:
Possible change:
Replace if-break by simply checking for if new.triangle != -9999.