Array-structured leaf returns

[ducky64]

... so we don't wrap every single integer in an object ...

Currently, when the tree returns a query and it hits leaves, it returns each leaf wrapped in an object (partly because Scala can't support union types). Instead, perhaps return a group of leaves as a new object, that slices the original array.

This can also be resolution sensitive: if two leaves are spaced apart greater than the requested resolution, it will return two arrays of size - even though they were both part of the same node in the B-tree's internal node structure.

This might actually be pretty negligible from a performance standpoint. At least until we get larger leaf widths.