Use Intervals as a way to reshape

Given intervals over time it would be great to be able to use them to split their respective continuous dimension (e.g. time) and make a new axis:

Shape `C x T` (5, 100) -> `C x interval_id x T_new` (5, 4, 25)

@dcherian suggests that what I want here would `groupby_construct`

In the case where the intervals are equal length this shouldn't be too hard. But if they are different lengths I think it will necessarily become a datatree?