stablesort: rework jump gathering The old code was buggy in some case, the new code give the same result as the 'headstart' version.

stablesort: stop recording jump type There are no mature user of this "jump type" data and the current implementation is known to be buggy. So we drop the logic for now. This will make on disk storage simpler. The data will be reintroduced later

stablesort: pass a jump recording function instead of a list This seems cleaner to abstract the underlying storage to the lower level. This also makes use more flexible about jump detection.