simplify display of RulesFor variants

[moritz-gross]

a small simplification using the strum crate that we already have.

[NSoiffer]

Looks good. I'm surprised that there aren't other places that can take advantage of that macros (or that it is not built-in).

[moritz-gross]

Looks good. I'm surprised that there aren't other places that can take advantage of that macros (or that it is not built-in).

there are multiple places that are close this, but not exactly fitting.

For example fmt of Token in infer_intent.rs is a close candidate, but we have the special case of
Token::ConceptOrLiteral(str) => format!("Literal({str})"),, which breaks the clean variant-based formatting.

Another case is "sapi5" for TTS::SAPI5 in prefs.rs, which switches from upper- to lowercase.

I could just make PRs based on what looks the cleanest and most consistent to me and then you can judge if it should be changed ?