Smarter implementation of iteration in `adaptor_increase_maxorder`

[mastricker]

Is (3,2,1) possible? If we plan to provide a proper full list of triplets, this should be included, right? Otherwise it is not really a full list? Or asked differently: What is the full triplet list? And is the (3,2,2) not entirely avoidable with the offset of the pair list iteration when searching for all the pairs?

_Originally posted by @mastricker in https://github.com/render_node/MDE3OlB1bGxSZXF1ZXN0UmV2aWV3MzIzNzc2Mjcy/pull_request_reviews/more_threads

[mastricker]

It should be possible to change the iteration decision to e.g. a start index with offset to avoid the self pair included in the triplet list by an int conversion depending on if the the self pair is present or not.

[mastricker]

Additional info: The resp. line is referenced. Proposition is that instead of checking for self pairs or not, the iteration over all the pairs while building >2 Order clusters should either start at the actual neighbour or at the self neighbour. This should in principle be possible by integer casting of the self pair variable into an offset.

Expected improvement is small, hence low-priority.