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.

stablesort: move into the stablerange module The stable range rely on the stable sort so it make senses to move it there. Will need direct access to it in the future.

subranges: migrate handling of single element range This is the simplest case by far, so we start with that one. We still use the rich object as an argument, but we'll do our best to not relying on that. This is important for performance reason.

stablerange: move the subrange cache into our new class This is the first step toward having more logic in that class