Add splice details to TransactionType::Splice

[jkczyz]

Surface splice broadcast metadata downstream, so consumers (notably LDK Node) can reconcile PaymentDetails / PendingPaymentDetails directly from the broadcaster callback.

• TransactionType::Splice now carries contribution: Option<FundingContribution> — our local contribution for this round, and replaced_txid: Option<Txid> — the prior negotiated candidate being replaced on RBF. The alternative (reacting to SplicePending) is worse: that event races with BDK wallet sync and doesn't carry the replaced txid.
• FundingContribution gains public getters for estimated_fee, inputs, and max_feerate; feerate is elevated from pub(super) to pub. Combined with existing value_added, outputs, change_output, this exposes everything a downstream consumer needs without reaching into the raw transaction.

The Hash derive on TransactionType is dropped (unused in the workspace; FundingContribution transitively contains ConfirmedUtxo which lacks Hash).

[ldk-reviews-bot]

👋 Thanks for assigning @wpaulino as a reviewer!
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Once they submit their review, I'll check if a second reviewer would be helpful.

[ldk-claude-review-bot]

I've thoroughly reviewed every file and hunk in the diff. Here is my assessment:

No issues found.

The core logic is correct:

• replaced_txid (channel.rs:9361-9364): Uses checked_sub(2) on the negotiated_candidates length after the current candidate has already been pushed (line 9338), correctly yielding the second-to-last entry's txid (the one being replaced). Returns None for the first splice (length 1), Some(prev_txid) for RBFs.

• contribution (channel.rs:9365): contributions.last().cloned() correctly returns the current round's contribution. The invariant that once contributions is non-empty, every subsequent completed round pushes a new entry is maintained by the tx_init_rbf flow (lines 13093-13125) and the abort cleanup in reset_pending_splice_state (line 7293).

• Hash derive removal: Justified since FundingContribution transitively contains ConfirmedUtxo which lacks Hash, and Hash was unused on TransactionType anywhere in the workspace.

• New public getters (estimated_fee, inputs, feerate, max_feerate): Visibility is consistent with the already-public value_added, outputs, and change_output getters. Types in the return positions (FundingTxInput, FeeRate, Amount) are all public.

• Test coverage: Comprehensive — covers first splice (None), single RBF (Some(first)), sequential RBFs (Some(prev)), tiebreak scenarios, acceptor-only and initiator-only contributions.