compat: in depth cache, only use cachevfs when available We support older version without the new vfs.

depthcache: issue a progress bar when loading the depth cache The operation can be in the minute order of magnitude of some larger repository. We better keep the user entertain when he wait.

depthcache: move to a dedicated object and storage The SQL cache was overkill and fragile. We move to a dedicated storage using the new generic class.

cache: adds debug details about what the content of the update Having more data in debug is good, we add a small method to help providing them. This code was headed for core during the 4.3 cycle but never made it there. So we starts with a copy in the evolve repository.

cache: introduce a changelogsourcebase class This abstract class will help code that need a cache tracking the changelog content (eg: the branchmap cache). The cache key used is the same as what the branchmap uses. This code was headed for core during the 4.3 cycle but never made it there. So we starts with a copy in the evolve repository.

cache: introduce an abstract class for cache we can upgrade incrementally Right now each class implements their own mechanism for validation, and update. We start introducing abstract class to ultimately allow more unification of the cache code. The end goal of this series is to introduce a cache for some obsolescence property, not to actually implement the cache. However, taking advantage of adding a new cache to introduce the abstract class seems like a win. This code was headed for core during the 4.3 cycle but never made it there. So we starts with a copy in the evolve repository.

depth: basic debugdepth implementation and test This will come very handy to validate more advanced implementation later.

topics: add a config to reject draft changeset without topic on a server This patch adds a new config option experimental.topic-mode.server which if sets to True, the server won't accept any draft changeset without topic on it. In case both `experimental.topic-mode.server` and `experimental.topic.publish-bare-branch` are set to True, the enforce-topic one is respected. Tests are added for it. The CHANGELOG file is also updated mentioning about the config option.