Aggregate multi-type calculation results

Implement calculateAll using a fold/map over the inputs list: map each CalculationInput to its result via a switch on formulaType (exhaustive — sealed class guarantees all cases handled), wrap each call in a try/catch to collect errors without crashing. The auto-approval logic should be extracted into a private _isAutoApprovalEligible(List items, ExpenseTypeConfig config) method for testability. The 50 km threshold check must sum ALL PerKmResult items in lineItems (there could be multiple if a claim has two separate mileage legs). The accounting export payload shape should be agreed with the Xledger/Dynamics integration team — use a flexible Map for now and replace with a typed class in a later integration task.

This is the hot path called on every BLoC state change (every expense type toggle), so keep it lean — no logging, no async, no DB access.

Write unit tests using flutter_test covering: (1) empty input list — zero result, autoApprovalEligible true, (2) single per-km input — correct delegation and result, (3) mixed inputs (per-km + flat receipt) — correct total and line items, (4) mileage exactly at 50 km threshold — autoApprovalEligible true, (5) mileage at 51 km — autoApprovalEligible false, (6) flat receipt with missing receipt — isIncomplete true on result, autoApprovalEligible false, (7) one formula throws — error is captured in calculationErrors, other line items still computed, (8) accountingExportPayload contains required fields, (9) three transit zones + two flat receipts — correct total sum. Aim for 90%+ branch coverage.