ortho: manage decomposition boxes as dynamic arrays

ortho: manage decomposition boxes as dynamic arrays

There is now no need to predict the number of horizontal and vertical
decomposition boxes upfront. The arrays for both are expanded on-demand.

This is a step towards resolving an issue where the upfront estimated trapezoid
count is exceeded, but this is likely an optimization for most workloads where
the estimation is not exceeded. Now fewer decomposition boxes will be allocated
because we generally do not need the full count that was estimated previously.

Gitlab: #56