b290b2950221578d73c3194a1accfd080f83631a test(chain): change test case comments to docstring (志宇)
c151d8fd230fb87f27aadb965157f94f01f021a2 fix(chain): `KeychainTxOutIndex::lookahead_to_target` (志宇)
Pull request description:
### Description
This method was not used (so it was untested) and it was not working. This fixes it.
The old implementation used `.next_store_index` which returned the keychain's last index stored in `.inner` (which include lookahead spks). This is WRONG because `.replenish_lookahead` needs the difference from last revealed.
### Changelog notice
Fix `KeychainTxOutIndex::lookahead_to_target`
### Checklists
#### All Submissions:
* [x] I've signed all my commits
* [x] I followed the [contribution guidelines](https://github.com/bitcoindevkit/bdk/blob/master/CONTRIBUTING.md)
* [x] I ran `cargo fmt` and `cargo clippy` before committing
#### Bugfixes:
* [x] I've added tests to reproduce the issue which are now passing
ACKs for top commit:
notmandatory:
ACK b290b2950221578d73c3194a1accfd080f83631a
Tree-SHA512: af50c6af18b6b57494cfa37f89b0236674fa331091d791e858f67b7d0b3a1e4e11e7422029bd6a2dc1c795914cdf6d592a14b42a62ca7c7c475ba6ed37182539
c3544c9b8c