Since we are now in serious business and publishing crates, let's move back to stable Rust.

https://twitter.com/en_JS/status/1676484656575946753

It would be really nice if it didn’t rely on nightly Rust. Nightly is cool for apps, but not for infra that others will build on.

To get started, change rust-toolchain.toml's channel to the latest <major.minor.patch>
(1.71.0) version, and run cargo check and fix all the code ;-)