Fix rust-analyzer problems seen with default features on Windows

I have set up arti on Windows with VS Code and rust-analyzer, mostly to see how well it is supported there.

The first things I've noticed and fixed in this merge request are problems which are highlighted right after cloning the repository.

With these fixes applied, only 4 problems remain, which result from an actual rust-analyzer bug as described here: https://github.com/rust-lang/rust-analyzer/issues/8434