Derive message formats macro support to string

[sbrugman]

Summary

Follow-up of #14090: the derive_message_formats macro previously did not support String::to_string. This PR changes the macro to require String::to_string instead of format! when no formatting parameters are provided.

There is room for further expansion of this macro, as this pattern used in #14090 is not yet supported for the message method:

let message = "message";
message.to_string();

Test Plan

cargo test and cargo expand, e.g. cargo expand rules::flake8_bandit::rules::jinja2_autoescape_false -p ruff_linter

[github-actions]

ruff-ecosystem results

Linter (stable)

✅ ecosystem check detected no linter changes.

Linter (preview)

✅ ecosystem check detected no linter changes.

[AlexWaygood]

Very nice! Just three places where I think you went slightly too far ;)

[sbrugman]

Fair point, reverted those three cases

[AlexWaygood]

LGTM. It might be worth @MichaReiser -- or somebody else who knows their Rust macros a little better -- also taking a look at the changes in ruff_macros, though 😄

[MichaReiser]

Hmm, I don't mind the change and it certainly helps that people don't learn the "bad" pattern of using format! over to_string` if there are no arguments.

At the other hand, to_string calls Display. So format! and to_string are equivalent. So this is a pure "esthetic" change. I'm okay with it because it doesn't add too much complexity to the macros and my main concern is with the macro itself (but that's a whole other story).