fix: yaml linting panic fixes

[jjroush]

Summary

This PR addresses lexar panics surfaced from #8330 as well as adding indentation diagnostics which were coupled with the panic test scenerios.

AI Disclosure: I paired on this ticket with Claude Code; this is a human cutting the PR.

Umbrella Linting Issue #2365

Test Plan

• Running these commits in reference to test(formatter/yaml): populate Prettier tests for YAML #8330; this PR resolves two panics that are seen from the yaml lexer.
  REPORT_PRETTIER=1 cargo test -p biome_yaml_formatter --test prettier_tests
• As a sanity check ran prettier and this biome change against examples in the aforementioned PR giving us the current state:

#	Input	Prettier (3.8.1)	Biome (this PR)	Aligned?
1	YAML 1.2.2 §7.4 — double-quoted implicit keys in flow sequence	parses, formats to "implicit block key": ["implicit flow key": value]	parses cleanly, no diagnostics	✅
2	YAML 1.2.2 §7.8 — single-quoted implicit keys in flow sequence	parses, formats to "implicit block key": ["implicit flow key": value]	parses cleanly, no diagnostics	✅
3	Insufficient indentation in flow collection	parse error: Insufficient indentation in flow collection	parse error: Insufficient indentation in flow collection (matching wording)	✅
4	Multi-line plain scalar inside flow sequence	parses, formats to xyz: [a bc]	parse error: expected ',' but instead found 'bc'	⚠️ pre-existing gap, see below

Cases 1 and 2 are the original panics this PR fixes. Case 3 is the new diagnostic this PR adds. Case 4 is documented as a known limitation tracked for follow-up — the lexer doesn't yet support multi-line plain scalars in flow context (crates/biome_yaml_parser/src/lexer/mod.rs:397 has the existing TODO).

[changeset-bot]

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[coderabbitai]

Walkthrough

The YAML lexer's flow collection handling now manages indentation breaches more gracefully. When flow collection content exits the parent block scope at nested depth, the lexer emits the "Insufficient indentation in flow collection" diagnostic exactly once, restores the cursor position, and continues processing trivia. Only when at root depth does it break from the loop. Test expectations were updated to reflect the new tokenisation behaviour in nested flow collections.

Suggested labels

A-Parser, L-Yaml

Suggested reviewers

• dyc3

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description check	✅ Passed	The description clearly relates to the changeset, documenting panic fixes, diagnostic additions, test results, and known limitations.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title 'fix: yaml linting panic fixes' accurately reflects the main objectives of addressing YAML lexer panics reported in #8330 and related linting issues.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[ematipico]

It would be great if we added a new file that covers the offending code that causes the panic. At the moment it's only a bunch of changes to existing files

[Eveeifyeve]

Even tho I am an outside OSS contributor, I see no issues with this apart from the stuff already mentioned.