feat(split): emit events for overfunding, penalty, deadline & whitelist changes (#686–689)

[Tisan1000]

What

Adds four indexer-facing events in contracts/split/src/events.rs and wires them into the relevant code paths in lib.rs, so payers and off-chain monitors can explain balance / state changes that were previously silent.

Issue	Event	Topics	Data
#686	overfunding_triggered	(split, ovf_trig, invoice_id)	(payer, policy, surplus, event_seq)
#687	penalty_applied	(split, pen_appl, invoice_id)	(payer, penalty_amount, penalty_bps, event_seq)
#688	deadline_extended	(split, dl_ext, invoice_id)	(old_deadline, new_deadline, event_seq)
#689	recipient_whitelist_updated	(split, rcp_wl_up, invoice_id)	(enabled, added, removed, event_seq)

#686 — overfunding policy

Emitted from _pay only when an AcceptAll or ReturnSurplus policy actually pushes funded past total:

• ReturnSurplus: surplus = stroops transferred straight back to the payer.
• AcceptAll: surplus = stroops accepted beyond the target (funded + credited - total).
• Cap is intentionally excluded — it defers to overflow_behavior, which already has its own events.

#687 — late-payment penalty

Emitted from the existing penalty branch in _pay when penalty_bps > 0 and penalty_deadline has passed, after the penalty has been distributed. penalty_amount is the actual amount deducted from the payment (amount * penalty_bps / 10_000).

#688 — deadline extension

Emitted from extend_deadline after the new deadline is persisted, carrying the previous value. Topics/data match the issue spec exactly.

#689 — recipient whitelist

Emitted from both add_to_recipient_whitelist and remove_from_recipient_whitelist whenever the list actually changes. added / removed are Vec<Address> (single entry in practice, vector leaves room for batch updates); enabled reflects recipient_whitelist_enabled. The pre-existing recipient_whitelisted / recipient_removed_from_whitelist events are left in place.

Tests

8 new unit tests in contracts/split/src/test.rs:

• overfunding event emitted for ReturnSurplus and AcceptAll, and not emitted on an exact fill (funded + payment == total)
• penalty event emitted for a late payment, not for an on-time one
• deadline event carries correct before/after values
• whitelist event on enable + add, and on remove

⚠️ Pre-existing build breakage on main

main does not currently compile. Fixing the four target issues surfaced this. There is one unclosed-delimiter merge artifact directly in the target file (events.rs) — a half-written duplicate invoice_expired — which this PR fixes, plus a duplicated use line in test.rs. Beyond that, main has ~39 further pre-existing compile errors from earlier bad merges that are unrelated to these issues and out of scope here, e.g.:

• duplicate mod validation; and a stale validation.rs / storage.rs using an old soroban-sdk API (Map::has, Vec::to_vec, Persistent::bump)
• missing calc_platform_fee / ContractError::TooFewRecipients
• InvoiceStatus::PayoutInProgress not handled in 6 match expressions
• invoice_refunded called with 3 args against a 2-arg definition
• env.storage().*.get() calls needing type annotations

Because of those, cargo test --workspace cannot build yet. The event functions and their call sites in this PR are self-contained, follow the existing events.rs conventions, and introduce no new errors.

Closes #686
Closes #687
Closes #688
Closes #689

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