stablerange: use first merge cache to skip over linear section If we are to skip over a large section of the range, skipping everything until the first merge seems like a good idea.

stablerange: add a new 'firstmerge' cache This cache store the first merge ancestors of a changesets. This is useful to avoid iteration over the changelog when building stablerange.

stablerange: drop unused `until` utility We no longer needs this function.

stablerange: use cached size data instead of walking the graph Less iteration is better.

stablesort: record previous segment size in the jump That was, we can skip over a full jump without walking it. We'll make use of this in the next changeset.

stablesort: move jump recording inside the exclusive function This will allow use to record to cache size of segment in a later changeset. If the exclusive set is empty, we need to record it outside that function.

stablerange: compute jump size after jump retrieval only This prepares the caching of jump sizes.

stablesort: warm jump cache more efficiently We no longer for a full depth iteration for all request: - we exit early for non-merge, - for merge, we only iterate over the exclusive area.

stablesort: use a regular dict for jumps This will help knowing what revision we have already queried or not.

stablerange: use the jump information for faster iteration Instead of doing a full iteration over the exclusive set, we compare the jump information instead. This perform the same kind of logic than before but will allow for much faster iteration once all the caches are in place.