revlog: create a iteration of a _InnerRevlog object within the revlog The goal of this object is to isolate a sub-API that can be implemented by a compiled object (e.g. Rust). So the boundary of this object will be arbitrary depending of what can we easily implemented in the Compiled code. For now, we start simple, and move the code that manage the IO objects in the inner object. More will come in the coming changesets. Note: the object definition could live in the different module to thin the `revlog.py` file, however there are other better candidate for extraction first and I have enought patch stacked on top of the this one for the split in this patch not to be worth it. So I leave this to future me.

revlog: drop the unused `_chunkcache` attribute Apparently, some time ago, the chunk cache moved in the randomaccessfile object.

revlog: drop the unused `_sidedatareadfp` method It has no caller anywhere and is probably the remains of some older code.

revlog: also migrates `revlog.upperboundcomp` to ConfigClass This was planned but overlooked when doing the rest of the migration.

revlog: small doc to the `files` method

revlog: remove the `_indexfp` method The method is only used two time and we want to move that code to a lower level object. So we simply inline the method to simplify further refactoring.

revlog: avoid opening and closing the file for each cloned revision The previous code was flushing files after each new revision, slowing things down. For exemple, with this change, the evolve repository can run `hg debugupgraderepo --run --optimize re-delta-parent` in about 3.4s instead of 4.5 seconds.

censor: accept censored revision during upgrade They can simply be passed by as censored.

censor: show that censored revision prevent repository upgrade This is not great.

stream-clone: fix a crash when a repo with an empty revlog is cloned

debug-delta-chain: print less data by default This is faster and simpler to read.

debugdeltachain: add a parameter to display all info This will be useful with the next changeset that change the defaul output to display the minimum amount of information.

debug-delta-chain: actually skip unrequested computation Doing quick test on mozilla-unified show we can run up to 2× faster by skipping some of these computation.

debug-delta-chain: add options to control what we compute Currently this mostly controls what we display, but actual computation saving will come soon.

debug-delta-chaing: add a parameter to select revision to look at This allows for much faster runtime when we are interrested in some revisions only.

delta-chain: extract some debugdeltachain logic is object Moving from a closure to an object's method will help us to extend the command logic.

delta-chain: move the debugdeltachain command in revlogutils There is a dedicated `mercurial.revlogutils.debug` module were this code fits well.

dirstate: document the `changing_*` context manager The methods that requires them have documentation, but the context themselves had none. This is now fixed.

revlog: deprecate the compatibility config property Now that core is no longer use them, we can deprecated them. Let us aim at removing them in the next version.

revlog: remove legacy usage of `_lazydeltabase` All core code is now getting the setting from the DeltaConfig object.

revlog: remove legacy usage of `_lazydelta` All core code is now getting the setting from the DeltaConfig object.

revlog: remove legacy usage of `canonical_parent_order` All core code is now getting the setting from the FeatureConfig object.

revlog: remove legacy usage of `_compute_rank` All core code is now getting the setting from the DeltaConfig object.

revlog: remove legacy usage of `_srmingapsize` All core code is now getting the setting from the DataConfig object.

revlog: remove legacy usage of `_srdensitythreshold` All core code is now getting the setting from the DataConfig object.

revlog: remove legacy usage of `hassidedata` All core code is now getting the setting from the FeatureConfig object.

revlog: remove legacy usage of `_sparserevlog` All core code is now getting the setting from the DeltaConfig object.

revlog: remove legacy usage of `_withsparseread` All core code is now getting the setting from the DeltaConfig object.

revlog: remove legacy usage of `_maxdeltachainspan` All core code is now getting the setting from the DeltaConfig object.

revlog: remove legacy usage of `_compengineopts` All core code is now getting the setting from the FeatureConfig object.