provide a non-destructive mechanism to determine if a sink/stream are paired #2358

Job	Run time
codegen	30s
cargo bench	1m 13s
cargo clippy	24s
cargo +stable build	37s
cargo +1.36 build (futures-{core, io, sink})	2m 35s
cargo +beta build	45s
cargo doc	19s
cargo hack check --feature-powerset	3m 39s
cargo +nightly build	1m 14s
cargo fmt	7s
cargo minimal-versions build	27s
cargo miri test	7m 7s
cargo build --target thumbv7m-none-eabi	29s
cargo test -Z sanitizer=address	5m 10s
cargo build --target thumbv6m-none-eabi	35s
cargo test -Z sanitizer=memory	3m 31s
cargo +1.56 build	1m 44s
cargo test (ubuntu-latest)	3m 9s
cargo test -Z sanitizer=thread	3m 30s
cargo test (macos-latest)	6m 25s
cargo test (windows-latest)	4m 10s
cargo test (ubuntu-latest, aarch64-unknown-linux-gnu)	4m 32s
cargo test (ubuntu-latest, armv7-unknown-linux-gnueabihf)	8m 13s
cargo test (ubuntu-latest, armv5te-unknown-linux-gnueabi)	9m 35s
cargo test (ubuntu-latest, i686-unknown-linux-gnu)	3m 11s
	1h 13m 11s

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