Remove horizontal scrolling in the rust code blocks

[1dimir]

• ~~Reduce max_width for rustfmt: 85 -> 81 - to fit into blocks with line numbers;~~
• Apply rustfmt for code chunks with long lines;
• Reorganize long use statement;
• Manually wrap long strings in macros;

#2012

[1dimir]

That's funny. 81 produces a lot of false positives and 85 wants to reconstruct back the wrapped expressions. And I'm not certain, if to use #[rustfmt::skip] for those is the right idea.

[mgeisler]

As mentioned in #2012, dprint fmt should be used to format both Rust and Markdown code consistently.

[mgeisler]

This PR might benefit from the work of @michael-kerscher in #2258. That is, perhaps the slide evaluator could also detect and flag scrollbars in code blocks?