peer-or-repo: make sure object in "scheme" have a `instance` object The previous form of having heterogeneous object in the dictionnary makes things more complicated than they needed to be. I am not super happy about the current (especially around 'islocal', that most item do not have), but this is already much better.

peer-or-repo: move the object setup in its own function The `_peerorrepo` function is problematic, because it can build different types of object (repository and peer). This make it hard to adjust the arguments to the type of object we needs. So this patch start a series of change to create peer and repo without going through a common function. We move the part of the function doing object setup it its own function to make it simpler to reuse in others contexts.

delta-find: use a single snapshot cache when applying a group to an object This will avoid walking the revlog over and over again in some situations. The difference is hard to show in our current benchmark suite, as the gain is lower than their overall instability.

delta-find: make sure we only use newer full snapshot as candidate The current code does not needs to protect against this, as there are no older snapshot in the current cache. However as we are getting ready to reuse this cache from one revision to another, we need the code to protect itself about what's coming.

delta-find: use sets instead of list in the snapshot cache This seems more appropriate.

delta-find: use a smarter object for snapshot caching This open the way for a longer lived cache.

find-delta: pass the cache-delta usage policy alongside the cache-delta The idea is to give higher level code more control to what will happens with the cache delta passed. This should help with controling how we treat delta's from different sources. The final goal of this change is to allow for server modes where the client can blindly accept any server delta without regards to any local constraints. This will be implemented in later changesets.

find-delta: move most of the debug-find-delta code in the debug module Lets us that module more. It will help us to keep revlog implementation details close to each other.

find-delta: minor preparatory change We are about to add more item in the cachedelta object, so lets access the item by index instead of doing a full extensions.

find-delta: rename _isgooddeltainfo Lets move to a more readable name now that we are allowed to. This cannot hurt.