sparse-revlog: stop using a heap to track selected gap Same logic as for 'gapsheap', we don't actually need a heap.

sparse-revlog: stop using a heap to track gaps The heap doesn't bring any performance advantage as we can simply sort the final list. Moreover, the lesser complexity helps a lot when we later implement it in C.

sparse-revlog: fast-path before computing payload size In this fast-path case, we do not need to compute the full delta chain payload. Since it comes with a significant cost, we avoid doing so if possible.

sparse-revlog: drop unused deltainfo parameter from segmentspan We no longer need to deal with slicing logic including uncommitted revision. We drop the associated code.