feat(delivery_contract): implement delivery cancellation and escrow r…

[rexx010]

Closes #24

Description

This PR introduces the secure delivery cancellation flow and resolves compilation/testing issues within the Escrow contract.

Key Changes

• Delivery Cancellation: Implemented cancel_delivery in the Delivery Contract with atomic cross-contract calls to trigger Escrow refunds (refund_escrow).
• State Machine Updates: Expanded DeliveryStatus to include InTransit, Delivered, and Cancelled. Added sender validation to DeliveryRecord.
• Event Emission Fix: Fixed missing &env arguments in escrow_contract for shared_types event emissions.
• Test Suite Modernization: Replaced deprecated register_contract with register and fixed event tuple index assertions across the test suites.

Testing

• Delivery cancellation state validation & atomic rollback tests added.
• All delivery_contract and escrow_contract tests pass successfully.

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