Simplify wallet persistence #5887

Job	Run time
Build and test (stable, true, --no-default-features)	3m 14s
Build and test (stable, true, --all-features)	3m 14s
Build Examples (example_cli)	14s
Build and test (1.63.0, --no-default-features)	4m 16s
Build Examples (example_bitcoind_rpc_polling)	25s
Build and test (1.63.0, --all-features)	4m 16s
Build Examples (example_electrum)	48s
Build Examples (example_esplora)	50s
Build Examples (wallet_electrum)	49s
Check no_std	12s
Build Examples (wallet_esplora_async)	51s
Build Examples (wallet_esplora_blocking)	55s
Check WASM	49s
Build Examples (wallet_rpc)	37s
clippy_check	28s
Rust fmt	8s
	22m 6s

Provide feedback