Collect Rust packages into a Cargo workspace

[andersk]

Description

This lets us run various Cargo commands across all packages automatically, manage all Rust dependencies in a shared Cargo.lock file, and significantly simplify the Nix package.

Reference

https://doc.rust-lang.org/cargo/reference/workspaces.html

Checklist

• [x] My code follows the style guidelines for this project
• [x] I have not added any packages that contain high risk or unknown licenses (GPL, LGPL, MPL, etc. consult with DevOps if in question)
• [x] I have performed a self review of my own code
• [ ] I have commented my code PARTICULARLY in hard to understand areas
• [ ] I have added thorough tests where needed