feat(chain): add get and range methods to CheckPoint

These methods allow us to query for checkpoints contained within the
linked list by height and height range. This is useful to determine
checkpoints to fetch for chain sources without having to refer back to
the `LocalChain`.

Currently this is not implemented efficiently, but in the future, we
will change `CheckPoint` to use a skip list structure.

crates/bdk/src/wallet/mod.rs

@@ -1127,18 +1127,14 @@ impl<D> Wallet<D> {
                 // anchor tx to checkpoint with lowest height that is >= position's height
                 let anchor = self
                     .chain
-                    .blocks()
                     .range(height..)
-                    .next()
+                    .last()
                     .ok_or(InsertTxError::ConfirmationHeightCannotBeGreaterThanTip {
                         tip_height: self.chain.tip().height(),
                         tx_height: height,
                     })
-                    .map(|(&anchor_height, &hash)| ConfirmationTimeHeightAnchor {
-                        anchor_block: BlockId {
-                            height: anchor_height,
-                            hash,
-                        },
+                    .map(|anchor_cp| ConfirmationTimeHeightAnchor {
+                        anchor_block: anchor_cp.block_id(),
                         confirmation_height: height,
                         confirmation_time: time,
                     })?;

crates/bitcoind_rpc/tests/test_emitter.rs

@@ -57,12 +57,15 @@ pub fn test_sync_local_chain() -> anyhow::Result<()> {
     }
 
     assert_eq!(
-        local_chain.blocks(),
-        &exp_hashes
+        local_chain
+            .iter_checkpoints()
+            .map(|cp| (cp.height(), cp.hash()))
+            .collect::<BTreeSet<_>>(),
+        exp_hashes
             .iter()
             .enumerate()
             .map(|(i, hash)| (i as u32, *hash))
-            .collect(),
+            .collect::<BTreeSet<_>>(),
         "final local_chain state is unexpected",
     );
 
@@ -110,12 +113,15 @@ pub fn test_sync_local_chain() -> anyhow::Result<()> {
     }
 
     assert_eq!(
-        local_chain.blocks(),
-        &exp_hashes
+        local_chain
+            .iter_checkpoints()
+            .map(|cp| (cp.height(), cp.hash()))
+            .collect::<BTreeSet<_>>(),
+        exp_hashes
             .iter()
             .enumerate()
             .map(|(i, hash)| (i as u32, *hash))
-            .collect(),
+            .collect::<BTreeSet<_>>(),
         "final local_chain state is unexpected after reorg",
     );