[bdk_chain_redesign] Implement OwnedIndexer for indexers

`SpkTxOutIndex` and `KeychainTxOutIndex` now both implement
`OwnedIndexer`.

crates/chain/src/keychain/txout_index.rs

@@ -1,6 +1,6 @@
 use crate::{
     collections::*,
-    indexed_tx_graph::Indexer,
+    indexed_tx_graph::{Indexer, OwnedIndexer},
     miniscript::{Descriptor, DescriptorPublicKey},
     ForEachTxOut, SpkTxOutIndex,
 };
@@ -111,6 +111,12 @@ impl<K: Clone + Ord + Debug + 'static> Indexer for KeychainTxOutIndex<K> {
     }
 }
 
+impl<K: Clone + Ord + Debug + 'static> OwnedIndexer for KeychainTxOutIndex<K> {
+    fn is_spk_owned(&self, spk: &Script) -> bool {
+        self.inner().is_spk_owned(spk)
+    }
+}
+
 impl<K: Clone + Ord + Debug> KeychainTxOutIndex<K> {
     /// Scans an object for relevant outpoints, which are stored and indexed internally.
     ///