feat!: rm persist submodule

Remove `PersistBackend`, `PersistBackendAsync`, `StageExt` and
`StageExtAsync`. Remove `async` feature flag and dependency. Update
examples and wallet.

example-crates/example_esplora/src/main.rs

@@ -4,7 +4,6 @@ use std::{
     sync::Mutex,
 };
 
-use bdk_chain::persist::PersistBackend;
 use bdk_chain::{
     bitcoin::{constants::genesis_block, Address, Network, Txid},
     indexed_tx_graph::{self, IndexedTxGraph},
@@ -362,6 +361,6 @@ fn main() -> anyhow::Result<()> {
 
     // We persist the changes
     let mut db = db.lock().unwrap();
-    db.write_changes(&(local_chain_changeset, indexed_tx_graph_changeset))?;
+    db.append_changeset(&(local_chain_changeset, indexed_tx_graph_changeset))?;
     Ok(())
 }