feat: add invoice event replay and contract-wide emergency withdrawal

[Idaonoli]

Summary

Implements two new contract features and resolves pre-existing compilation errors that had accumulated across recent PRs.

closes #232 — Invoice payment event replay for indexer recovery

• replay_invoice_events(invoice_id) is a pure read+emit function callable by anyone. It re-emits the full historical event sequence for an invoice so an offline indexer can resync from a single call:
  • One invoice_created (replay) event
  • One payment_received (replay) event per entry in invoice.payments, in original order
  • The terminal status event (invoice_released or invoice_refunded, replay) when the invoice is no longer Pending
• All four replay event emitters carry a fourth replay topic so indexers can distinguish them from live events and skip double-counting.
• No state mutation — safe for any caller at any time.

closes #233 — Contract-wide emergency withdrawal

• EmergencyWithdraw(Address, Address) added to TimelockAction.
• request_emergency_withdraw(admin, token, destination) — requires SuperAdmin auth and the contract to already be paused. Queues the withdrawal in the existing timelock system and returns the action_id.
• execute_action handles the new variant with two additional guards beyond the normal timelock check:
  • Mandatory 7-day minimum delay (enforced independently of the configured timelock_secs)
  • Contract must still be paused at execution time
• On success, transfers the full token balance from the contract to destination and emits emergency_withdrawal_executed (token, destination, amount).

Pre-existing compilation fixes

Several earlier PRs left the codebase in a non-compiling state. These are fixed minimally as a prerequisite:

• types.rs: removed duplicate min_funding_amount, priorities, and admin_frozen fields from Invoice; added missing creation_timestamp and min_payment_increment to InvoiceExt2 so they round-trip through storage; wired external_prerequisite through Invoice::split, Invoice::assemble, and Invoice::from_legacy.
• events.rs: removed eight duplicate function definitions (each function appeared twice with slightly different event symbol names).
• lib.rs: removed a duplicate SHARD_COUNT constant, two redundant require_admin function definitions, a duplicate admin_frozen field assignment in clone_invoice, and updated all bare InvoiceExt2 default literals to include the new fields.
• test.rs: added missing external_prerequisite: None to the invoice_options helper.

Test plan

• test_replay_invoice_events_pending — confirms 2 replay events for a Pending invoice (created + 1 payment, no terminal event)
• test_replay_invoice_events_released — confirms 4 replay events for a Released invoice (created + 2 payments + released)
• test_emergency_withdraw_blocked_when_unpaused — request panics when contract is active
• test_emergency_withdraw_blocked_before_7_days — execute panics before the 7-day delay elapses
• test_emergency_withdraw_succeeds_after_7_days — full balance transferred to destination after pause + 7-day delay, balance verified on both sides
• All existing cargo tests pass
• cargo clippy passes with zero warnings

Closes #232
Closes #233
Closes #234
Closes #235

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