Merge bitcoindevkit/bdk#1034: Implement linked-list LocalChain and update chain-src crates/examples

b206a985cf fix: Even more refactoring to code and documentation (志宇)
bea8e5aff4 fix: `TxGraph::missing_blocks` logic (志宇)
db15e03bdc fix: improve more docs and more refactoring (志宇)
95312d4d05 fix: docs and some minor refactoring (志宇)
8bf7a997f7 Refactor `debug_assertions` checks for `LocalChain` (志宇)
315e7e0b4b fix: rm duplicate `bdk_tmp_plan` module (志宇)
af705da1a8 Add exclusion of example cli `*.db` files in `.gitignore` (志宇)
eabeb6ccb1 Implement linked-list `LocalChain` and update chain-src crates/examples (志宇)

Pull request description:

  Fixes #997
  Replaces #1002

  ### Description

  This PR changes the `LocalChain` implementation to have blocks stored as a linked-list. This allows the data-src thread to hold a shared ref to a single checkpoint and have access to the whole history of checkpoints without cloning or keeping a lock on `LocalChain`.

  The APIs of `bdk::Wallet`, `esplora` and `electrum` are also updated to reflect these changes. Note that the `esplora` crate is rewritten to anchor txs in the confirmation block (using the esplora API's tx status block_hash). This guarantees 100% consistency between anchor blocks and their transactions (instead of anchoring txs to the latest tip). `ExploraExt` now has separate methods for updating the `TxGraph` and `LocalChain`.

  A new method `TxGraph::missing_blocks` is introduced for finding "floating anchors" of a `TxGraph` update (given a chain).

  Additional changes:

  * `test_local_chain.rs` is refactored to make test cases easier to write. Additional tests are also added.
  * Examples are updated.
  * Exclude example-cli `*.db` files in `.gitignore`.
  * Rm duplicate `bdk_tmp_plan` module.

  ### Notes to the reviewers

  This is the smallest possible division of #1002 without resulting in PRs that do not compile. Since we have changed the API of `LocalChain`, we also need to change `esplora`, `electrum` crates and examples alongside `bdk::Wallet`.

  ### Changelog notice

  * Implement linked-list `LocalChain`. This allows the data-src thread to hold a shared ref to a single checkpoint and have access to the whole history of checkpoints without cloning or keeping a lock on `LocalChain`.
  * Rewrote `esplora` chain-src crate to anchor txs to their confirmation blocks (using esplora API's tx-status `block_hash`).

  ### 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 b206a985cf

Tree-SHA512: a513eecb4f1aae6a5c06a69854e4492961424312a75a42d74377d363b364e3d52415bc81b4aa3fbc3f369ded19bddd07ab895130ebba288e8a43e9d6186e9fcc

crates/chain/src/keychain.rs

@@ -11,10 +11,7 @@
 //! [`SpkTxOutIndex`]: crate::SpkTxOutIndex
 
 use crate::{
-    collections::BTreeMap,
-    indexed_tx_graph::IndexedAdditions,
-    local_chain::{self, LocalChain},
-    tx_graph::TxGraph,
+    collections::BTreeMap, indexed_tx_graph::IndexedAdditions, local_chain, tx_graph::TxGraph,
     Anchor, Append,
 };
 
@@ -85,24 +82,33 @@ impl<K> AsRef<BTreeMap<K, u32>> for DerivationAdditions<K> {
     }
 }
 
-/// A structure to update [`KeychainTxOutIndex`], [`TxGraph`] and [`LocalChain`]
-/// atomically.
-#[derive(Debug, Clone, PartialEq)]
+/// A structure to update [`KeychainTxOutIndex`], [`TxGraph`] and [`LocalChain`] atomically.
+///
+/// [`LocalChain`]: local_chain::LocalChain
+#[derive(Debug, Clone)]
 pub struct LocalUpdate<K, A> {
-    /// Last active derivation index per keychain (`K`).
-    pub keychain: BTreeMap<K, u32>,
+    /// Contains the last active derivation indices per keychain (`K`), which is used to update the
+    /// [`KeychainTxOutIndex`].
+    pub last_active_indices: BTreeMap<K, u32>,
+
     /// Update for the [`TxGraph`].
     pub graph: TxGraph<A>,
+
     /// Update for the [`LocalChain`].
-    pub chain: LocalChain,
+    ///
+    /// [`LocalChain`]: local_chain::LocalChain
+    pub chain: local_chain::Update,
 }
 
-impl<K, A> Default for LocalUpdate<K, A> {
-    fn default() -> Self {
+impl<K, A> LocalUpdate<K, A> {
+    /// Construct a [`LocalUpdate`] with a given [`local_chain::Update`].
+    ///
+    /// [`CheckPoint`]: local_chain::CheckPoint
+    pub fn new(chain_update: local_chain::Update) -> Self {
         Self {
-            keychain: Default::default(),
-            graph: Default::default(),
-            chain: Default::default(),
+            last_active_indices: BTreeMap::new(),
+            graph: TxGraph::default(),
+            chain: chain_update,
         }
     }
 }
@@ -122,6 +128,8 @@ impl<K, A> Default for LocalUpdate<K, A> {
 )]
 pub struct LocalChangeSet<K, A> {
     /// Changes to the [`LocalChain`].
+    ///
+    /// [`LocalChain`]: local_chain::LocalChain
     pub chain_changeset: local_chain::ChangeSet,
 
     /// Additions to [`IndexedTxGraph`].