Audit Rust dependencies for version updates or replacements

There is an outstanding PR for removing/moving unused dependencies, but this is a separate suggestion to look at dependencies that may be stale, or may have been moved to stdlib.

The simplest example, Tokio moved from `num_cpus` to `std::thread::available_parallelism`, so that could be something worth looking at.

Also, `lazy_static` has proposed a std alternative that could be looked into.