Reformat code and introduce rustfmt check in CI

[MarijnS95]

Hi! I'd love to start contributing to this crate, but one little annoyance is that it doesn't seem to use Rust's standard rustfmt autoformatter yet, and all code is out of sync. If there's no particular reason for that, I'd like to format the code and introduce a check in CI to ensure the code in the main branch as well as new code introduced by external contributors follows the same formatting guidelines.

[kornelski]

A while ago I've converted standalone functions to methods, and I wanted to keep the diff minimal to ensure I'm not changing anything else, and forgot to fix the formatting later.

[MarijnS95]

All fine, that makes a lot of sense.

I was going to suggest using rustfmt config options to tweak it to make the changes less invasive but you've already done so on the main branch.

I don't understand the addition of disable_all_formatting = true though, that seems to be disabling most of the functionality?