build(testenv): make "miniscript" feature default #33

Job	Run time
Rust fmt	16s
prepare	6s
Check WASM	1m 2s
Check no_std	22s
Build & Test (1.88.0, true, --all-features)	3m 41s
Build & Test (1.63.0, --all-features)	3m 55s
Build & Test (1.88.0, true, --no-default-features --features miniscript/no-std,bdk_chain/hashbrown)	1m 20s
Build & Test (1.75.0, --no-default-features --features miniscript/no-std,bdk_chain/hashbrown)	1m 21s
Build & Test (1.75.0, --all-features)	3m 57s
Build & Test (1.63.0, --no-default-features --features miniscript/no-std,bdk_chain/hashbrown)	1m 59s
Build & Test Examples (example_cli)	23s
Build & Test Examples (example_esplora)	57s
Build & Test Examples (example_bitcoind_rpc_polling)	46s
Build & Test Examples (example_electrum)	1m 13s
Rust clippy	1m 18s
	22m 36s

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