Update mdbook to version 0.4.52 (#2870)

The most significant change for users is that the search index is
downloaded on demand.

For us as a project, it’s good to see the server used by `mdbook serve`
change from `warp` to `asum`: the former hadn’t been updated in a while,
leading us to have old dependencies in our `Cargo.lock`.

I also ran `cargo update` to further unify the versions of our
dependencies. This shrunk `cargo tree --duplicates` a little more.

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Co-authored-by: Michael Kerscher <[email protected]>

Author: mgeisler