feat(css_formatter): CssPropertyAtRule formatting

[denbezrukov]

Summary

Implement CssPropertyAtRule formatting

Test Plan

cargo test

[netlify]

✅ Deploy Preview for biomejs ready!

Name	Link
🔨 Latest commit	f4cd786
🔍 Latest deploy log	https://app.netlify.com/sites/biomejs/deploys/660084a758f5740008ef5cb6
😎 Deploy Preview	https://deploy-preview-2181--biomejs.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.
Lighthouse	1 paths audited Performance: 100 (🟢 up 5 from production) Accessibility: 97 (no change from production) Best Practices: 100 (no change from production) SEO: 93 (no change from production) PWA: - View the detailed breakdown and full score reports

---

To edit notification comments on pull requests, go to your Netlify site configuration.

[codspeed-hq]

CodSpeed Performance Report

Merging #2181 will degrade performances by 12.02%

_{⚠️ No base runs were found}

_{Falling back to comparing feat/css-property-at-rule-formatting (f4cd786) with main (a2027da)}

Summary

❌ 1 regressions
✅ 92 untouched benchmarks

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Benchmarks breakdown

	Benchmark	main	feat/css-property-at-rule-formatting	Change
❌	eucjp.json[uncached]	5 ms	5.7 ms	-12.02%