Mark all format-like macros for Clippy

[nyurik]

Allows Clippy to lint format-like usage of non-standard macros

See https://doc.rust-lang.org/nightly/clippy/attribs.html#clippyformat_args

[nyurik]

It seems this is due to rust-lang/rust#98291 - it might mean the actual macros are being declared incorrectly by Slint, but there is no warning about it because of a bug in the compiler? Or that the compiler simply doesn't have a good error message for this. Or ... TBD.

[ogoffart]

Thanks for the PR, looks nice.
Too bad this causes compilation error. My intuition tells me the compiler think that #[clippy::...] is a macro.
Perhaps it could be worked around by adding a #[cfg_attr(clippy, ...)] or something like this?