refactor(markdown): deduplicate shared helper functions

[jfmcdowell]

Note

This PR was created with AI assistance (Claude Code).

Summary

Extract two duplicated helper functions into shared pub(crate) definitions:

• is_whitespace_only: was identical in list.rs, quote.rs, and mod.rs. Now lives once in syntax/mod.rs.
• find_line_start: was identical in token_source.rs and fenced_code_block.rs. Now lives once in token_source.rs.

No behavior change.

Test Plan

• just test-crate biome_markdown_parser — all passed
• just test-markdown-conformance — 652/652
• just f
• just l

Docs

N/A.

[changeset-bot]

⚠️ No Changeset found

Latest commit: 7180db4

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[codspeed-hq]

Merging this PR will not alter performance

✅ 28 untouched benchmarks
⏩ 228 skipped benchmarks¹

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_{Comparing jfmcdowell:refactor/markdown-deduplicate-helpers (7180db4) with main (716e4e1)}

Footnotes

1. 228 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]

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ℹ️ Recent review info

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📥 Commits

Reviewing files that changed from the base of the PR and between 20e2000 and 7180db4.

📒 Files selected for processing (1)

• crates/biome_markdown_parser/src/syntax/list.rs

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Walkthrough

This PR centralises two previously duplicated helpers in the markdown parser by making find_line_start (from token_source.rs) and is_whitespace_only (from syntax/mod.rs) pub(crate) and updating fenced_code_block.rs, list.rs, and quote.rs to import and use those shared implementations instead of local copies. No public API signatures were changed.

Possibly related PRs

• PR #9730: Modifies fenced code block closing-fence detection and virtual_line_start handling, using the same consolidated find_line_start logic.
• PR #9740: Adjusts HTML block parsing around virtual_line_start validation; shares the same helper-consolidation pattern for line-start logic.

Suggested reviewers

• dyc3
• ematipico

🚥 Pre-merge checks | ✅ 2

✅ Passed checks (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately summarises the main change: deduplicating shared helper functions across the markdown parser modules.
Description check	✅ Passed	The description clearly relates to the changeset, detailing which functions were deduplicated, where they now live, and providing test coverage evidence.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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