stablerange: compute subranges from parent when possible Unless we are a merge, we can infer the standard subranges of a range by reusing the subranger of its parent. We update the implementation to do so. We still needs the "old way" for merge. We move that code in a dedicated function for the sake of simplicity.

stablerange: add an official warmup function The function is responsible for making sure we have the necessary data for a sets of heads. For now this only warm the depth cache. More will follow soon. Such explicite warmup will be usefull for on disck caching as an early point of writing will be easier.

stablerange: remove now unnecessary setter The class is handling all computations and cache access by itself now. So we can drop this method.

stablerange: directly perform slicing in the getting method Now that all necessary functions are available, we simply apply the standard slicing on cache miss and proceed.

stablerange: move standard slice point definition in main class More migration of code away from the doomed individual class.

stablerange: move the slicing method on the central class We migrate code away for the individual range class.

stablerange: move the range class in the new module Our ultimate goal is to remove this class for performance reason. however for now, it contains most of the code we care about so we migrate it as a block first.