No longer compiling on nightly rust 1.82.0

[Oberdiah]

is_sorted has been stabilized (rust-lang/rust#128279), so the polyfilled methods in polyfill.rs are no longer compiling due to name conflicts on the std iterator trait.

As an aside, I love this crate! I was pulling my hair out for hours trying to implement this behaviour with wrapper types and Ord and it was just a huge mess - this has made things 10x easier, so thanks!