feat(wallet): support Testnet4 in valid networks #6629

Job	Run time
prepare	3s
Rust fmt	13s
Check no_std	37s
Build and test (1.83.0, true, --no-default-features --features miniscript/no-std)	2m 17s
Check WASM	1m 22s
Build & Test Examples (example_cli)	35s
Build and test (1.83.0, true, --all-features)	3m 57s
Build & Test Examples (example_bitcoind_rpc_polling)	36s
clippy_check	1m 13s
Build and test (1.63.0, --no-default-features --features miniscript/no-std)	4m 23s
Build & Test Examples (example_electrum)	50s
Build and test (1.63.0, --all-features)	5m 59s
Build & Test Examples (example_esplora)	53s
Build & Test Examples (example_wallet_electrum)	50s
Build & Test Examples (example_wallet_esplora_async)	1m 1s
Build & Test Examples (example_wallet_esplora_blocking)	56s
Build & Test Examples (example_wallet_rpc)	36s
	26m 21s

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