Merge bitcoindevkit/bdk#1812: fix(wallet): use `map_keychain` in `Wal… #6681

Job	Run time
prepare	4s
Rust fmt	11s
Build & Test (1.84.0, true, --no-default-features --features miniscript/no-std)	1m 36s
Check WASM	41s
Check no_std	18s
Build & Test (1.84.0, true, --all-features)	3m 44s
Rust clippy	33s
Build & Test (1.63.0, --no-default-features --features miniscript/no-std)	2m 9s
Build & Test Examples (example_cli)	20s
Build & Test Examples (example_bitcoind_rpc_polling)	30s
Build & Test (1.63.0, --all-features)	4m 8s
Build & Test Examples (example_electrum)	51s
Build & Test Examples (example_esplora)	58s
Build & Test (1.75.0, --no-default-features --features miniscript/no-std)	1m 32s
Build & Test (1.75.0, --all-features)	3m 47s
Build & Test Examples (example_wallet_electrum)	53s
Build & Test Examples (example_wallet_esplora_async)	55s
Build & Test Examples (example_wallet_esplora_blocking)	57s
Build & Test Examples (example_wallet_rpc)	31s
	24m 38s

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