feat: `select!` macro for no-std environments #2955

Job	Run time
cargo +stable build	31s
cargo +1.56 build	1m 5s
cargo test (ubuntu-latest)	2m 41s
cargo +1.36 build (futures-{core, io, sink})	36s
cargo +beta build	42s
cargo test (macos-latest)	5m 8s
cargo +nightly build	37s
cargo test (windows-latest)	4m 53s
cargo bench	56s
cargo clippy	14s
cargo test (ubuntu-latest, aarch64-unknown-linux-gnu)	3m 37s
cargo miri test	5m 8s
cargo test (ubuntu-latest, armv7-unknown-linux-gnueabihf)	5m 7s
cargo build --target thumbv7m-none-eabi	20s
cargo test (ubuntu-latest, armv5te-unknown-linux-gnueabi)	5m 7s
cargo test -Z sanitizer=address	3m 25s
cargo build --target thumbv6m-none-eabi	16s
cargo test (ubuntu-latest, i686-unknown-linux-gnu)	4m 25s
cargo test -Z sanitizer=memory	5m 6s
cargo test -Z sanitizer=thread	2m 28s
cargo doc	17s
cargo hack check --feature-powerset	20s
cargo fmt	5s
cargo minimal-versions build	23s
	53m 27s

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