Deprecate this crate when Rust 1.81 is released?

[tony-iqlusion]

Rust 1.81 will stabilize the error_in_core feature: https://releases.rs/docs/1.81.0/#1810-beta

This will make the Error trait stable as core::error::Error: https://doc.rust-lang.org/beta/core/error/trait.Error.html

I believe this crate's raison d'etre was working around the unavailability of this trait in no_std contexts. Now it should be possible to use the Error trait ubiquitously regardless of if std is available or not.