feat: copy_bidirectional_with_timeout added

[dilitvinov]

Add read-idle drain timeout to copy_bidirectional

Problem

poll_splice_drain waits for the source to become readable with no upper bound. If the remote peer stops sending data without closing the connection, the task parks indefinitely — no CPU is wasted, but the connection is never cleaned up.

Solution

Introduce an optional read-idle timeout for the drain phase.

API

copy_bidirectional_with_timeout(&mut sl, &mut sr, Duration::from_secs(30)).await?;

No timeout is applied by default — existing behaviour is unchanged, no breaking changes.

Any suggestions are welcomed!

[dilitvinov]

@cxw620 please, have a look 🙏

[cxw620]

I will test it locally when I have free time on this weekend. CI is broken because tracing-subscriber and its dependency time does not follow the MSRV they claim, please don't mind. Thank you for your work!