See also previous #78 .

One question is which dice to reroll at each stage.

If depth = 'inf', the mode is lowest/highest, and the roller is permitted to choose, the roller would choose to reroll just the single lowest/highest die at each stage. At some point they might choose to stop rolling early, if it looks like they are unlikely to improve on the current set. At this point it becomes a full-blown optimization problem, which seems too much for a single built-in method.

We could force the roller to reroll as many dice as possible, and then fall back to mode when the rerolls run out. Or the max_rerolls could apply separately to each depth level.