96a9aa6 feat(chain): refactor `merge_chains` (志宇)
2f22987 chore(chain): fix comment (志宇)
daf588f feat(chain): optimize `merge_chains` (志宇)
77d3595 feat(chain)!: rm `local_chain::Update` (志宇)
1269b06 test(chain): fix incorrect test case (志宇)
72fe65b feat(esplora)!: simplify chain update logic (志宇)
eded1a7 feat(chain): introduce `CheckPoint::insert` (志宇)
519cd75 test(esplora): move esplora tests into src files (志宇)
a6e613e test(esplora): add `test_finalize_chain_update` (志宇)
494d253 feat(testenv): add `genesis_hash` method (志宇)
886d72e chore(chain)!: rm `missing_heights` and `missing_heights_from` methods (志宇)
bd62aa0 feat(esplora)!: remove `EsploraExt::update_local_chain` (志宇)
1e99793 feat(testenv): add `make_checkpoint_tip` (志宇)

Pull request description:

  Fixes #1354

  ### Description

  Built on top of both #1369 and #1373, we simplify the `EsploraExt` API by removing the `update_local_chain` method and having `full_scan` and `sync` update the local chain in the same call. The `full_scan` and `sync` methods now takes in an additional input (`local_tip`) which provides us with the view of the `LocalChain` before the update. These methods now return structs `FullScanUpdate` and `SyncUpdate`.

  The examples are updated to use this new API. `TxGraph::missing_heights` and `tx_graph::ChangeSet::missing_heights_from` are no longer needed, therefore they are removed.

  Additionally, we used this opportunity to simplify the logic which updates `LocalChain`. We got rid of the `local_chain::Update` struct (which contained the update `CheckPoint` tip and a `bool` which signaled whether we want to introduce blocks below point of agreement). It turns out we can use something like `CheckPoint::insert` so the chain source can craft an update based on the old tip. This way, we can make better use of `merge_chains`' optimization that compares the `Arc` pointers of the local and update chain (before we were crafting the update chain NOT based on top of the previous local chain). With this, we no longer need the `Update::introduce_older_block` field since the logic will naturally break when we reach a matching `Arc` pointer.

  ### Notes to the reviewers

  * Obtaining the `LocalChain`'s update now happens within `EsploraExt::full_scan` and `EsploraExt::sync`. Creating the `LocalChain` update is now split into two methods (`fetch_latest_blocks` and `chain_update`) that are called before and after fetching transactions and anchors.
  * We need to duplicate code for `bdk_esplora`. One for blocking and one for async.

  ### Changelog notice

  * Changed `EsploraExt` API so that sync only requires one round of fetching data. The `local_chain_update` method is removed and the `local_tip` parameter is added to the `full_scan` and `sync` methods.
  * Removed `TxGraph::missing_heights` and `tx_graph::ChangeSet::missing_heights_from` methods.
  * Introduced `CheckPoint::insert` which allows convenient checkpoint-insertion. This is intended for use by chain-sources when crafting an update.
  * Refactored `merge_chains` to also return the resultant `CheckPoint` tip.
  * Optimized the update `LocalChain` logic - use the update `CheckPoint` as the new `CheckPoint` tip when possible.

  ### 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

  #### New Features:

  * [x] I've added tests for the new feature
  * [x] I've added docs for the new feature

ACKs for top commit:
  LLFourn:
    ACK 96a9aa6

Tree-SHA512: 3d4f2eab08a1fe94eb578c594126e99679f72e231680b2edd4bfb018ba1d998ca123b07acb2d19c644d5887fc36b8e42badba91cd09853df421ded04de45bf69

b45897e feat(electrum): update docs and simplify logic of `ElectrumExt` (志宇)
92fb6cb chore(electrum): do not use `anyhow::Result` directly (志宇)
b2f3cac feat(electrum): include option for previous `TxOut`s for fee calculation (Wei Chen)
c0d7d60 feat(chain)!: use custom return types for `ElectrumExt` methods (志宇)
2945c6b fix(electrum): fixed `sync` functionality (Wei Chen)
9ed33c2 docs(electrum): fixed `full_scan`, `sync`, and crate documentation (Wei Chen)
b1f861b feat: update logging of electrum examples (志宇)
a6fdfb2 feat(electrum)!: use new sync/full-scan structs for `ElectrumExt` (志宇)
653e4fe feat(wallet): cache txs when constructing full-scan/sync requests (志宇)
58f27b3 feat(chain): introduce `TxCache` to `SyncRequest` and `FullScanRequest` (志宇)
721bb7f fix(chain): Make `Anchor` type in `FullScanResult` generic (志宇)
e3cfb84 feat(chain): `TxGraph::insert_tx` reuses `Arc` (志宇)
2ffb656 refactor(electrum): remove `RelevantTxids` and track txs in `TxGraph` (Wei Chen)

Pull request description:

  Fixes #1265
  Possibly fixes #1419

  ### Context

  Previous changes such as

  * Universal structures for full-scan/sync (PR #1413)
  * Making `CheckPoint` linked list query-able (PR #1369)
  * Making `Transaction`s cheaply-clonable (PR #1373)

  has allowed us to simplify the interaction between chain-source and receiving-structures (`bdk_chain`).

  The motivation is to accomplish something like this ([as mentioned here](#1153 (comment))):
  ```rust
  let things_I_am_interested_in = wallet.lock().unwrap().start_sync();
  let update = electrum_or_esplora.sync(things_i_am_interested_in)?;
  wallet.lock().unwrap().apply_update(update)?:
  ```

  ### Description

  This PR greatly simplifies the API of our Electrum chain-source (`bdk_electrum`) by making use of the aforementioned changes. Instead of referring back to the receiving `TxGraph` mid-sync/scan to determine which full transaction to fetch, we provide the Electrum chain-source already-fetched full transactions to start sync/scan (this is cheap, as transactions are wrapped in `Arc`s since #1373).

  In addition, an option has been added to include the previous `TxOut` for transactions received from an external wallet for fee calculation.

  ### Changelog notice

  * Change `TxGraph::insert_tx` to take in anything that satisfies `Into<Arc<Transaction>>`. This allows us to reuse the `Arc` pointer of what is being inserted.
  * Add `tx_cache` field to `SyncRequest` and `FullScanRequest`.
  * Make `Anchor` type in `FullScanResult` generic for more flexibility.
  * Change `ElectrumExt` methods to take in `SyncRequest`/`FullScanRequest` and return `SyncResult`/`FullScanResult`. Also update electrum examples accordingly.
  * Add `ElectrumResultExt` trait which allows us to convert the update `TxGraph` of `SyncResult`/`FullScanResult` for `bdk_electrum`.
  * Added an option for `full_scan` and `sync` to also fetch previous `TxOut`s to allow for fee calculation.

  ### 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

  #### New Features:

  * [x] I've added tests for the new feature
  * [x] I've added docs for the new feature

ACKs for top commit:
  ValuedMammal:
    ACK b45897e
  notmandatory:
    ACK b45897e

Tree-SHA512: 1e274546015e7c7257965b36079ffe0cb3c2c0b7c2e0c322bcf32a06925a0c3e1119da1c8fd5318f1dbd82c2e952f6a07f227a9b023c48f506a62c93045d96d3