Generalise `reduce_flags` into `tuple<bool, _>`

[SSoelvsten]

While solving #412 , I created the reduce_flags class to hold a tuple of bool values inside of a single unsigned integer. This class should be generalised into a specialialisation of the tuple template in adiar/internal/data_types/tuple.h (with associated unit tests).

[SSoelvsten]

This first is relevant when #479 is merged with main.