Look into tools for auditing Unsafe rust

[ounsworth]

As we use more Unsafe, we should looking into CI tooling.

Miri is a tool for checking unsafe rust for undefined behaviour (like, out-of-bounds writes).

Cargo-anneal checks your unsafe code by constructing a formal model.

borrow-sanitizer

cargo-careful

[ounsworth]

At the moment, this is a bit overkill since we only have 3 lines of unsafe rust and 0 lines of asm in the whole library. So more food-for-future thought.

Relates to #131