fix(editor): cross browser test stability (#14897)

#### PR Dependency Tree


* **PR #14897** 👈

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

* **Bug Fixes**
* Improved reliability of shape and connector detection by forcing full
DOM renders during waits.
* Fixed race conditions in code-block theme loading and cleanup when
components unmount.
* Refined viewport element discovery to correctly handle
rotated/canvas-layer elements and avoid stale DOM removal.

* **Tests**
  * Increased polling timeouts and retries to reduce flakiness.
* Disabled per-file parallelism and ensured test setup performs full
cleanup before starting; extended test timeout.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

blocksuite/integration-test/src/__tests__/utils/setup.ts

@@ -127,6 +127,8 @@ export async function setupEditor(
   const options: SetupEditorOptions = optionsInput ?? {};
   const enableDomRenderer = options?.enableDomRenderer ?? false;
 
+  await cleanup();
+
   const collection = new TestWorkspace(createCollectionOptions());
   collection.storeExtensions = storeExtensions;
   collection.meta.initialize();