bvh_span

The binary radix tree over sorted Morton codes: for internal node i, zero_span_of(i) gives the run of sorted places it covers and the place it splits at, as a ZeroSpan (lo, hi, split: the left child covers lo .. split, the right split + 1 .. hi), from the length of the common prefix of the sorted codes (zero_delta, equal codes ordered by place). The module header lists the buffers and the param the includer declares.