Simplify wallet persistence #5886

Job	Run time
Build and test (stable, true, --no-default-features)	2m 58s
Build Examples (example_cli)	18s
Build and test (stable, true, --all-features)	3m 1s
Build Examples (example_bitcoind_rpc_polling)	34s
Build and test (1.63.0, --no-default-features)	3m 2s
Check no_std	10s
Build Examples (example_electrum)	59s
Check WASM	41s
Build and test (1.63.0, --all-features)	2m 44s
Build Examples (example_esplora)	45s
Build Examples (wallet_electrum)	45s
clippy_check	31s
Rust fmt	10s
Build Examples (wallet_esplora_async)	52s
Build Examples (wallet_esplora_blocking)	43s
Build Examples (wallet_rpc)	29s
	18m 42s

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