Announcing Rust 1.86.0

Rust 1.86.0 has been released, introducing new features such as trait upcasting, support for indexing multiple elements mutably in HashMaps and slices, and allowing safe functions to be marked with the #[target_feature] attribute. Additionally, debug assertions for non-null pointers have been implemented, and a target deprecation warning has been issued for the i586-pc-windows-msvc target in the next version. Various APIs have also been stabilized in this release.