ref(chain)!: create module indexer

and replace keychain module with `balance.rs`

crates/esplora/src/async_ext.rs

@@ -231,7 +231,7 @@ async fn chain_update<A: Anchor>(
 }
 
 /// This performs a full scan to get an update for the [`TxGraph`] and
-/// [`KeychainTxOutIndex`](bdk_chain::keychain::KeychainTxOutIndex).
+/// [`KeychainTxOutIndex`](bdk_chain::indexer::keychain_txout::KeychainTxOutIndex).
 async fn full_scan_for_index_and_graph<K: Ord + Clone + Send>(
     client: &esplora_client::AsyncClient,
     keychain_spks: BTreeMap<

crates/esplora/src/blocking_ext.rs

@@ -213,7 +213,7 @@ fn chain_update<A: Anchor>(
 }
 
 /// This performs a full scan to get an update for the [`TxGraph`] and
-/// [`KeychainTxOutIndex`](bdk_chain::keychain::KeychainTxOutIndex).
+/// [`KeychainTxOutIndex`](bdk_chain::indexer::keychain_txout::KeychainTxOutIndex).
 fn full_scan_for_index_and_graph_blocking<K: Ord + Clone>(
     client: &esplora_client::BlockingClient,
     keychain_spks: BTreeMap<K, impl IntoIterator<Item = Indexed<ScriptBuf>>>,