C++ refactoring: ak.argcombinations, ak.combinations

[ioanaif]

No description provided.

[codecov]

Codecov Report

Merging #1307 (589b4e7) into main (5613d44) will increase coverage by 0.07%.
The diff coverage is 77.77%.

Impacted Files	Coverage Δ
...ard/_v2/operations/structure/ak_argcombinations.py	76.92% <70.00%> (+1.92%)	⬆️
...wkward/_v2/operations/structure/ak_combinations.py	90.90% <87.50%> (+15.90%)	⬆️
src/awkward/_v2/contents/listoffsetarray.py	80.55% <0.00%> (+0.13%)	⬆️
src/awkward/_v2/contents/indexedoptionarray.py	86.77% <0.00%> (+0.16%)	⬆️
src/awkward/_v2/contents/listarray.py	88.23% <0.00%> (+0.21%)	⬆️
src/awkward/_v2/contents/content.py	81.78% <0.00%> (+0.31%)	⬆️
src/awkward/_v2/contents/regulararray.py	83.81% <0.00%> (+0.81%)	⬆️
src/awkward/_v2/operations/structure/ak_argsort.py	100.00% <0.00%> (+25.00%)	⬆️

[jpivarski]

Fantastic! I guess combinations was already implemented as a layout method, and just needed to be passed through to highlevel (and tested)? It's great to know that it's tested now.