feat(css): allow scss declarations in @page blocks

[denbezrukov]

Summary

Allow SCSS declarations inside @page blocks, including nested property declarations (font:
{ ... }) and SCSS variables in page margin at-rules (for example @top-left).

Test Plan

1. cargo test -p biome_css_parser
2. cargo test -p biome_css_formatter

[changeset-bot]

⚠️ No Changeset found

Latest commit: 26261a7

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[codspeed-hq]

Merging this PR will not alter performance

✅ 29 untouched benchmarks
⏩ 126 skipped benchmarks¹

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_{Comparing db/scss-page-declarations (26261a7) with next (7a36937)}

Footnotes

1. 126 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

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Walkthrough

This PR extends SCSS support within CSS @page at-rules by introducing two new declaration variants (ScssDeclaration and ScssNestingDeclaration) to the grammar. The parser has been updated to handle SCSS nesting declarations in page at-rule contexts, the formatter routes both variants through their respective format methods, and bogus block handling has been added. Test files demonstrate the new functionality with variable scoping and nested properties in @page rules.

Possibly related PRs

• fix(css): improve parsing recovery when encountering qualified rules inside CSS @page at-rule blocks #8905: Modifies the same page at-rule files to add qualified and bogus handling for AnyCssPageAtRuleItem variants
• feat(css): support scss nesting declarations in declaration lists #9135: Directly adds SCSS nesting declaration support including updates to AnyCssPageAtRuleItem parsing and formatting

Suggested reviewers

• siketyan
• ematipico

🚥 Pre-merge checks | ✅ 2

✅ Passed checks (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately describes the main change: adding SCSS declaration support to @page blocks, which aligns with all modified files.
Description check	✅ Passed	The description clearly outlines the feature (SCSS declarations in @page blocks) and includes a test plan, directly relating to the changeset.

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✨ Finishing Touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch db/scss-page-declarations

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