Merge bitcoindevkit/bdk#1946: chore: create and apply rustfmt.toml #7189

Job	Run time
Rust fmt	13s
prepare	3s
Check no_std	17s
Build & Test (1.86.0, true, --no-default-features --features miniscript/no-std,bdk_chain/hashbrown)	1m 10s
Rust clippy	25s
Build & Test (1.86.0, true, --all-features)	3m 23s
Check WASM	49s
Build & Test (1.75.0, --no-default-features --features miniscript/no-std,bdk_chain/hashbrown)	1m 51s
Build & Test (1.75.0, --all-features)	3m 45s
Build & Test (1.63.0, --no-default-features --features miniscript/no-std,bdk_chain/hashbrown)	6m 39s
Build & Test Examples (example_bitcoind_rpc_polling)	36s
Build & Test Examples (example_electrum)	54s
Build & Test (1.63.0, --all-features)	8m 3s
Build & Test Examples (example_esplora)	51s
Build & Test Examples (example_cli)	18s
	29m 17s

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