feat: implement atomic swap contract for peer-to-peer key exchanges

[AzahasTech]

Overview

This PR implements an atomic swap contract for peer-to-peer creator key exchanges, enabling two parties to swap key allocations in a single transaction. It adds a propose/accept/cancel lifecycle with counterparty restrictions, a 1-hour expiry with automatic unlock, and the three required lifecycle events.

Related Issue

Changes

🔁 Atomic Swap Contract

• [MODIFY] creator-keys/src/curve_subscriptions_swaps.rs

  • propose_swap(offered_key, offered_amount, requested_key, requested_amount, counterparty) — locks the proposer's offered amount and records the proposal with its counterparty and expiry.
  • accept_swap(proposal_id) — counterparty-only; atomically transfers both sides of the swap.
  • cancel_swap(proposal_id) — proposer-only; releases the locked offered amount back to the proposer.
  • 1-hour expiry on proposals, with automatic unlock of locked amounts once expired.

• [MODIFY] creator-keys/src/events.rs

  • Adds SwapProposed, SwapExecuted, and SwapCancelled event definitions carrying proposal and amount data.

Verification Results

cargo build -p creator-keys
✅ Compiles cleanly

cargo test -p creator-keys
✅ Swap lifecycle tests passed (propose, accept, cancel, expiry)

Acceptance Criteria	Status
accept_swap correctly transfers both sides atomically	✅ Both sides transferred in a single execution path
cancel_swap releases locked amounts to proposer	✅ Locked offered amount released to proposer
Proposal expires correctly after 1h with automatic unlock	✅ Expiry enforced at 1h with automatic unlock
accept_swap restricted to specified counterparty	✅ Counterparty-only guard enforced
All three events emitted with correct proposal and amount data	✅ SwapProposed, SwapExecuted, SwapCancelled emitted

Closes #1072

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