Tracking Issue for Rust rewrite

Hi,

This issue will track design discussions for the Rust rewrite. I already have a byte-for-byte compatible drop in re-implementation with formal verification (excluding the crossing of the FFI boundary) to adjust.

@simo5 Mentioned "not caring" for Async code, but unfortunately the LibVerto dependency is functionally that already. I'm open to using the [MIO](https://github.com/tokio-rs/mio) library which underpins Tokio to use lower level primitives, but unless we are targeting embedded devices I don't see a reason why we can't depend on Tokio itself. I don't consider this a personal blocker, and can rewrite things as requested.