test: migrate test & utils (#14569)

#### PR Dependency Tree


* **PR #14569** 👈

This tree was auto-generated by
[Charcoal](https://github.com/danerwilliams/charcoal)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **Chores**
* Upgraded development test tooling to Vitest v4 and added Playwright
browser test integration; normalized test configurations and CI shard
matrix.

* **Tests**
* Added a large suite of new integration tests covering editor flows
(edgeless, database, embeds, images, latex, code, clipboard,
multi-editor, presentation, undo/redo, etc.).
* Removed numerous end-to-end Playwright test suites across the same
feature areas.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

blocksuite/affine/blocks/code/src/highlight/affine-code-unit.ts

@@ -45,8 +45,10 @@ export class AffineCodeUnit extends ShadowlessElement {
     if (!codeBlock || !vElement) return plainContent;
     const tokens = codeBlock.highlightTokens$.value;
     if (tokens.length === 0) return plainContent;
+    const line = tokens[vElement.lineIndex];
+    if (!line) return plainContent;
     // copy the tokens to avoid modifying the original tokens
-    const lineTokens = structuredClone(tokens[vElement.lineIndex]);
+    const lineTokens = structuredClone(line);
     if (lineTokens.length === 0) return plainContent;
 
     const startOffset = vElement.startOffset;