zorch.sumcheck.jagged.rounds

Scheme-agnostic per-round helpers for jagged sumcheck: the virtual-mass correction, the Gruen coefficient-form round polynomial, and the eq-slice expansion. Degree-agnostic — they take the interpolation constants (naturals/inv_vand) as arguments (also the round marker's operands, so the crossing stays inline here rather than routing through gruen.round_coeffs, which would rebuild them and DCE the operands out of the composite). The LSB bind is sumcheck.domain.fold(..., msb=False). The LogUp-specific combine + plane bodies live in zorch.logup_gkr._jagged_rounds.