try object arrays for perioddata

[wpbonelli]

up to now the prototype has separated period data into an array for each column of the period data record (OC is a little different but same spirit). this makes unstructuring/writing to input files harder because the arrays must be recombined or cleverly indexed, and it also departs from the DFN files, which will mean we need some extra translations during codegen. try following the DFNs exactly and using arrays of object dtype. this makes indexing/etc a little more awkward. hope this helps us consider the tradeoffs and decide which approach is ideal.

[wpbonelli]

Despite the challenges this presents in transformation before writing MF6 list-based input, it seems best to keep array variables separate. The fact that they are combined as records in the DFN specification is a formatting detail, not a core requirement.