Merge bitcoindevkit/bdk#1403: Update `bdk_electrum` crate to use sync/full-scan structs

b45897e6fe2f7e67f5d75ec6f983757b28c5ec19 feat(electrum): update docs and simplify logic of `ElectrumExt` (志宇)
92fb6cb37387fb0b9fe5329e772f0d928a33e116 chore(electrum): do not use `anyhow::Result` directly (志宇)
b2f3cacce6081f3bf6e103d1d2ca0707c545a67e feat(electrum): include option for previous `TxOut`s for fee calculation (Wei Chen)
c0d7d60a582b939324bb48ec8c5035020ec90699 feat(chain)!: use custom return types for `ElectrumExt` methods (志宇)
2945c6be88b3bf5105afeb8addff4861f0458b41 fix(electrum): fixed `sync` functionality (Wei Chen)
9ed33c25ea01278b0a47c8ecd5ea6fa33119a977 docs(electrum): fixed `full_scan`, `sync`, and crate documentation (Wei Chen)
b1f861b932afd5e490c0814b1921b97cc2f1d912 feat: update logging of electrum examples (志宇)
a6fdfb2ae4caa1cdd23aa5e5ffaf02716473a98e feat(electrum)!: use new sync/full-scan structs for `ElectrumExt` (志宇)
653e4fed6d16698bc5859c1e4afdcee7b3d83dad feat(wallet): cache txs when constructing full-scan/sync requests (志宇)
58f27b38eb2093bb9b715b7e0ebd1619ecad74ee feat(chain): introduce `TxCache` to `SyncRequest` and `FullScanRequest` (志宇)
721bb7f519131ca295a00efa2d242b4923e2bddd fix(chain): Make `Anchor` type in `FullScanResult` generic (志宇)
e3cfb84898cfa79d4903cf276fc69ffb0605b4d4 feat(chain): `TxGraph::insert_tx` reuses `Arc` (志宇)
2ffb65618afb7382232a3c08a077dd1109005071 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](https://github.com/bitcoindevkit/bdk/issues/1153#issuecomment-1752263555)):
  ```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 b45897e6fe2f7e67f5d75ec6f983757b28c5ec19
  notmandatory:
    ACK b45897e6fe2f7e67f5d75ec6f983757b28c5ec19

Tree-SHA512: 1e274546015e7c7257965b36079ffe0cb3c2c0b7c2e0c322bcf32a06925a0c3e1119da1c8fd5318f1dbd82c2e952f6a07f227a9b023c48f506a62c93045d96d3