Don't include footer row in example values during mapping

[rossjones]

Currently during mapping we identify the data range to select some examples from, but the call that is made expects an inclusive range, and we want an exclusive one. Due to the lack of options wrt range types we instead just decrement the range we want to retrieve.

We may want to consider having different range types to avoid having to add/subtract one based on requirements, and perhaps make iteration and calculations easier

[simonwo]

Is there any milage in always using an inclusive/exclusive definition of ranges?

[rossjones]

Is there any milage in always using an inclusive/exclusive definition of ranges?

I think generally we have inclusive ranges, but there are cases where we don't want that and it feels error prone to have to determine that on a case by case, and make sure we bound any loops with <= or < than the upper bound of the range. It feels a lot easier to have a default of inclusive range, and allow a exclusive range type for those other cases. We don't need to keep track of intent and if they both have a iteration trait we can traverse the ranges without fear of getting it wrong.