feat: `select!` macro for no-std environments #2998

Job	Run time
cargo +1.36 build (futures-{core, io, sink})	45s
cargo +stable build	42s
cargo minimal-versions build	23s
cargo +beta build	41s
cargo bench	45s
cargo +nightly build	32s
cargo build --target thumbv7m-none-eabi	19s
cargo test (ubuntu-latest)	2m 2s
cargo +1.63 build	1m 11s
cargo build --target thumbv6m-none-eabi	16s
cargo test (macos-latest)	2m 4s
cargo clippy	23s
cargo doc	18s
cargo test (windows-latest)	1m 56s
cargo test (ubuntu-latest, aarch64-unknown-linux-gnu)	2m 4s
cargo hack check --feature-powerset	21s
cargo test (ubuntu-latest, armv7-unknown-linux-gnueabihf)	2m 3s
cargo fmt	14s
cargo test (ubuntu-latest, armv5te-unknown-linux-gnueabi)	2m 4s
cargo miri test	2m 4s
cargo test (ubuntu-latest, i686-unknown-linux-gnu)	2m 4s
cargo test -Z sanitizer=address	2m 3s
cargo test -Z sanitizer=memory	2m 3s
cargo test -Z sanitizer=thread	2m 3s
	29m 20s

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