fix(cg): unify Stylo test locks to prevent cascading test failures

[softmarshmallow]

Summary

• The html and htmlcss test modules each had their own mutex guarding Stylo's process-global DOM slot. Since both locks protected the same shared state, tests from the two modules could run concurrently and corrupt Stylo, causing panics that poisoned the htmlcss lock (which used .unwrap()) and cascaded to all 22 htmlcss tests.
• Consolidate into a single stylo_test::lock() in lib.rs with poison recovery via unwrap_or_else(|e| e.into_inner()), matching the pattern html already used.
• Fixes the cargo test failure on main after feat(htmlcss): CSS Grid layout + box-shadow support #635 was merged.

Test plan

• cargo test -p cg passes (683 lib tests, 0 failures)
• cargo test --workspace --exclude grida-canvas-wasm passes
• CI test-crates workflow passes

🤖 Generated with Claude Code

Summary by CodeRabbit

• Refactor
  • Consolidated test infrastructure for HTML-related modules to use a shared synchronization mechanism.

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No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 4c01598b-d498-4ced-8581-e799804c8395

📥 Commits

Reviewing files that changed from the base of the PR and between f4ffe54 and 7dd831c.

📒 Files selected for processing (3)

• crates/grida-canvas/src/html/mod.rs
• crates/grida-canvas/src/htmlcss/mod.rs
• crates/grida-canvas/src/lib.rs

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Walkthrough

This change refactors test synchronization across the grida-canvas crate. A new centralized test-locking module (stylo_test) is added to provide a shared Mutex<()> with poison-recovery logic. Local test mutexes in the html and htmlcss modules are removed and replaced with calls to this shared lock function.

Changes

Cohort / File(s)	Summary
Test Synchronization Infrastructure crates/grida-canvas/src/lib.rs	Added new stylo_test module with process-global STYLO_TEST_LOCK and public lock() function that recovers from poisoned mutex states via unwrap_or_else().
Test Lock Migration crates/grida-canvas/src/html/mod.rs, crates/grida-canvas/src/htmlcss/mod.rs	Removed local Mutex<()> definitions (HTML_TEST_LOCK and TEST_LOCK) from test modules. Updated all HTML and HTML/CSS tests to call crate::stylo_test::lock() instead of local lock acquisitions.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and specifically describes the main change: unifying Stylo test locks to prevent cascading failures. It directly reflects the core objective of consolidating separate mutexes into a single crate-level lock.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
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• Create PR with unit tests
• Commit unit tests in branch feature/unruffled-vaughan

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