Refactor/use iterators to preselect utxos #6607

Job	Run time
prepare	3s
Rust fmt	13s
Check no_std	1m 9s
Build and test (1.83.0, true, --no-default-features --features miniscript/no-std)	1m 20s
Build and test (1.83.0, true, --all-features)	1m 20s
Check WASM	1m 30s
Build and test (1.63.0, --no-default-features --features miniscript/no-std)	1m 12s
clippy_check	1m 1s
Build and test (1.63.0, --all-features)	1m 5s
Build & Test Examples (example_cli)	30s
Build & Test Examples (example_bitcoind_rpc_polling)	1m 7s
Build & Test Examples (example_electrum)	56s
Build & Test Examples (example_esplora)	53s
Build & Test Examples (example_wallet_electrum)	53s
Build & Test Examples (example_wallet_esplora_async)	57s
Build & Test Examples (example_wallet_esplora_blocking)	1m 28s
Build & Test Examples (example_wallet_rpc)	42s
	16m 19s

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