Heads-up: Using #[bench] on stable is becoming a hard error

[RalfJung]

Hi there! This crate showed up in a crater report for rust-lang/rust#134273. We are planning to de-stabilize the accidentally stable #[bench] attribute, which breaks the build of punkt 1.0.5. (ferristseng/rust-punkt#15 would fix that but apparently has never been released to crates.io.) You should already have seen warnings about this since Rust 1.77; soon this will likely be a hard error.