Function reverse 

pub fn reverse(
    original: &SettlementResult,
    grund: KorrekturGrund,
) -> SettlementResult

Create a reversal (Stornorechnung) of a prior settlement.

All positions are negated. The result references the original via correction_of. No re-calculation is performed — the reversal is a pure mirror of the original, ensuring auditability.

Usage

let reversal = reverse(&original, grid_billing::KorrekturGrund::Messwertkorrektur);
assert_eq!(reversal.total_eur, -original.total_eur);