stablesort: rename function to stablesort_branchpoint We are about to test different approach to stable sorting. We clarify that the existing method is sorting from branch points.

stablerange: update the filename to avoid cache confusion The schema validation seems to not work as well as intended, we update the file name to make sure there will be no confusion.

stablesort: extract in its own module We are going to introduce variants, cache and more complex logic, we move that in its own repository beforehand.