stablerange: remove call to 'repo.revs' It turned out that the percentage of time spend parsing the revset string was two digits, so we compute de heads inline.

stablerange: reuse node calculation as much as possible We have a property cache with that value, so we just reuse it.

stablerange: adds some caching of the subranges The goal of subranges is to be as reusable as possible, so we cache the subrange relationship to take advantage of this.

stablerange: operate on an unfiltered repository We only do operation on ancestors so using unfiltered is fine.

depth: use lower lever function to compute missing The time spend parsing the revset is noticeable.

depth: update depth to code to reuse ancestors depth Computing the depth of all N revs is no longer 'O(N**2)'

obsdiscovery: extract a smarted depth in utility The function is reusing previous depth for ancestors unless this is a merge.

obsdiscovery: simply some of the missing computation

discovery: implement some range based discovery This use the previously implemented methods to implement some discovery and fetch method using ranges. There is currently major performance issue and some aspect of the protocol will changes.

discovery: introduce a official 'obshash associated to a range The hash in a combination of the hash a its subrange. If the range is a leaf, we have the obsmarker relevant to the node in that leaf range.