style(edition): migrate the codebase to the 2024 Style Edition

[rami3l]

This PR is the first part of rustup's migration to Rust 2024, which contains style-related changes only. Notably, macro invocations are now correctly formatted by rustfmt.

A second PR will follow shortly once this one gets merged, which will perform a semi-auto migration based on #4061's plan:

[workspace.lints.rust]
rust_2018_idioms = { level = "deny", priority = -1 }
rust-2024-compatibility = { level = "warn", priority = -2 }

PS: The newly-added rustfmt config is here for migration purposes. It should be deleted by the end of the second PR.

PPS: The CI should pass once the 2024 Edition lands in stable in a few hours.

[ChrisDenton]

Seems fine. Though did something about maximum line length change? In any case using the new style seems like a good idea.

[rami3l]

@ChrisDenton I believe what's really happening is that rustfmt is now trying its best to make macro invocations behave like function invocations, and there used to be many macro invocation lines that are too wide but got ignored.

[ChrisDenton]

Ah that makes sense.