Add `*-stock` theory method

[Junior]

This was the first method attempted, which didn't have enough foundations to remain stable and consistent as it's siblings evolved. Now that the secondary methods are becoming more and more native, by declaring the returning index as the pivot point, this allows shelf stock method to return with a similar intent.

This method relies on a first come, first serve basis in that it acts as a queue - so applying the theory of blind-stock doesn't make sense at this time, as it'd likely end up more like blind-auction except the players are the ones being moved around.

Eventually these theories would be exported as functions themselves, with the need to ensure consistency as well as speed with scale.