feat: add utility to test last_seen persistence #15

Job	Run time
prepare	3s
Rust fmt	16s
Check no_std	29s
Rust clippy	28s
Build & Test (1.87.0, true, --no-default-features --features miniscript/no-std,bdk_chain/hashbrown)	1m 17s
Build & Test (1.63.0, --no-default-features --features miniscript/no-std,bdk_chain/hashbrown)	2m 9s
Build & Test Examples (example_bitcoind_rpc_polling)	35s
Build & Test (1.75.0, --no-default-features --features miniscript/no-std,bdk_chain/hashbrown)	1m 56s
Build & Test (1.63.0, --all-features)	2m 7s
Build & Test Examples (example_electrum)	1m 8s
Check WASM	1m 45s
Build & Test Examples (example_cli)	26s
Build & Test (1.87.0, true, --all-features)	1m 54s
Build & Test Examples (example_esplora)	54s
Build & Test (1.75.0, --all-features)	2m 1s
	17m 28s

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