[huangji6693-max]

Summary

Implements on-chain dispute resolution with multi-arbitrator quorum voting (open_dispute, vote_dispute, resolve_dispute) for StellarSplit.

Closes #344

Key Changes

1. Arbitrator Set & Quorum Configuration:
   • set_arbitrators(env, admin, arbitrator_set, quorum_threshold) allows the admin to configure the designated arbitrator set and quorum threshold (e.g. 2-of-3), stored under arbitrator_set_key() (arb_set) and quorum_threshold_key() (arb_quor).
   • Query helpers: get_arbitrator_set(env) and get_quorum_threshold(env).
2. Dispute Lifecycle Entry Points:
   • open_dispute(env, invoice_id, payer, reason): Opens a dispute on an invoice, freezes the invoice (invoice.disputed = true, blocking release and refund), stores ArbitrationDispute under dispute_key(invoice_id) (("dispute", invoice_id)), and emits DisputeOpened.
   • vote_dispute(env, invoice_id, arbitrator, approve): Verifies the caller is in arbitrator_set, rejects duplicate votes from the same arbitrator, tallies approve_votes / reject_votes, and emits DisputeVoteCast.
   • resolve_dispute(env, invoice_id): Permissionless crank callable by anyone once approve_votes + reject_votes >= quorum_threshold. Resolves according to majority vote (approve_votes > reject_votes releases funds to recipients; reject_votes > approve_votes refunds all payers) and emits DisputeResolved.
3. Storage Key Snapshot & Migration Note:
   • Added dispute_key, arbitrator_set_key, and quorum_threshold_key to contracts/split/src/storage_snapshot.rs and updated tests/snapshots/storage_keys.json (verified collision-free).
4. Unit Tests (issue_344_tests):
   • test_dispute_arbitration_open_vote_resolve_approve_path
   • test_dispute_arbitration_open_vote_resolve_reject_path
   • test_dispute_arbitration_duplicate_vote_rejected
   • test_dispute_arbitration_non_arbitrator_vote_rejected
   • test_dispute_arbitration_non_existent_invoice_rejected
   • test_dispute_freezes_refund_while_open