Order Cleanup

Implements issue #214 as a small helper contract around the existing order_handler storage and cancellation flow.

What it adds

• set_order_expiry(...) to configure timeout by order type.
• cancel_expired_order(...) callable by anyone after the timeout.
• preview_expired_order(...) for read-only status checks.
• record_manual_refund(...) as an audit event for admin/manual recovery when an order record is already gone.

Integration requirement

Grant this helper contract the ORDER_KEEPER role so it can call order_handler.cancel_order after it verifies expiry. The existing handler then refunds collateral and removes the order from indexes.

Default

Unset expiry uses 2880, matching the requested default.