cancel_tx has no effect

[ErikDeSmedt]

Describe the bug

The cancel_tx method does not free up the change.

To Reproduce
See https://github.com/ErikDeSmedt/bdk-gists/blob/master/tests/cancel_takes_effect.rs

Expected behavior
I expect that the change is freed

Build environment

• BDK tag/commit: bdk_wallet 1.0.5
• OS+version: debian
• Rust/Cargo version: 1.79.0

Additional context

[notmandatory]

I think the issue you're running into is a misunderstanding of what cancel_tx does. That function only frees up the script index of the change address if they haven't been seen as used/spent by the wallet via broadcast/sync OR by manually inserting them into the wallet tx graph as you've done with apply_unconfirmed_txs.

    /// Informs the wallet that you no longer intend to broadcast a tx that was built from it.
    ///
    /// This frees up the change address used when creating the tx for use in future transactions.
    // TODO: Make this free up reserved utxos when that's implemented
    pub fn cancel_tx(&mut self, tx: &Transaction) {
        let txout_index = &mut self.indexed_graph.index;
        for txout in &tx.output {
            if let Some((keychain, index)) = txout_index.index_of_spk(txout.script_pubkey.clone()) {
                // NOTE: unmark_used will **not** make something unused if it has actually been used
                // by a tx in the tracker. It only removes the superficial marking.
                txout_index.unmark_used(*keychain, *index);
            }
        }
    }

[evanlinjin]

I think we should probably rename cancel_tx to unreserve_change_address.