zorch.sumcheck.jagged.layout

Scheme-agnostic segment-layout recurrences for jagged sumcheck.

The numpy gather that remaps a jagged row_counts layout across a fold, and the even-prepad/folded-count recurrence. Both are host-side (numpy / pure Python) so the schedule is precomputed and baked into the frx trace as a constant. Shared by the jagged round schedule and the LogUp-GKR circuit transition.