Update bdk_electrum crate to use sync/full-scan structs

[LagginTimes]

Fixes #1265
Possibly fixes #1419

Context

Previous changes such as

• Universal structures for full-scan/sync (PR Introduce universal sync/full-scan structures for spk-based syncing #1413)
• Making CheckPoint linked list query-able (PR feat(chain): add get and range methods to CheckPoint #1369)
• Making Transactions cheaply-clonable (PR Wrap transactions as Arc<Transaction> in TxGraph #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):

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 Arcs 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 TxOuts to allow for fee calculation.

Checklists

All Submissions:

• I've signed all my commits
• I followed the contribution guidelines
• I ran cargo fmt and cargo clippy before committing

New Features:

• I've added tests for the new feature
• I've added docs for the new feature

[ValuedMammal]

Looking good so far.

I made a note related to adding the client as a parameter to determine_tx_anchor - you may have already considered this. I see you mentioned potentially doing more batch calls, which is a good idea assuming we can ensure the results are in order consistent with the request.

side note: the commit message could use an extra newline after the subject and before the body.

[evanlinjin]

It's great that the API is simplified now. However, with the current changes, every call to ElectrumExt::full_scan forces us to download every full tx?

EDIT: Ahh, I see your TODOs in your description.

[evanlinjin]

For the commit message, remember to put a new line between first line and body.

[evanlinjin]

It seems that you intended the sync flow to be:

1. Copy the wallet's TxGraph and pass it to the chain source.
2. Perform update, and populate TxGraph with missing transactions/anchors and return it back to the wallet.

However, the downsides of this approach is the following:

1. Because we are cloning the wallet's TxGraph, and TxGraph stores both transactions and anchors, and only transactions are cheaply copied (not anchors), therfore copying the TxGraph over is non-optimal.
2. The anchors that are copied from the wallet cannot be used anyway. We need to keep the anchor type in the TxGraph a generic to support all wallet types. However, we wish to return an update TxGraph with the ConfirmationTimeHeightAnchor to represent all information available from Electrum. We cannot guarantee that the wallet's anchor type can be transformed into ConfrimastionTimeHeightAnchor, therefore we end up just re-fetching the anchors from Electrum anyway.

Hence, I think it is better to have a transaction cache HashMap<Txid, Arc<Transaction>> and the TxGraph update as a separate concept.

[evanlinjin]

ACK 4ccd86a

[evanlinjin]

This needs a rebase, merging #1203 broke this.

[ValuedMammal]

ACK b45897e

[notmandatory]

ACK b45897e

Tested with examples: example_electrum and wallet_electrum