revlog: move the_revisioncache on the inner object The goal for this inner object is to compute that things we cache, it make more sense to have the inner object handle it directly.

revlog: move the `deltachain` method on the inner object This is a necessary step before being able to move more logic around restoring a revision content there. For now, we do a simple patch for the perf extension logic, when the implementation of the inner object changes, we will likely need some evolution of the API. However this is true of many things in the perf extension. So we will see this later.