Generic associated types to be stable in Rust 1.65

As of Rust 1.65, which is set to release on November 3rd, generic associated types (GATs) will be stable — over six and a half years after the original RFC was opened. This is truly a monumental achievement; however, as with a few of the other monumental features of Rust, like async or const generics, there are limitations in the initial stabilization that we plan to remove in the future. The goal of this post is not to teach about GATs, but rather to briefly introduce them to any readers that m...