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/ext-loader/package.json

@@ -15,7 +15,7 @@
     "zod": "^3.25.76"
   },
   "devDependencies": {
-    "vitest": "^3.2.4"
+    "vitest": "^4.0.18"
   },
   "exports": {
     ".": "./src/index.ts"

blocksuite/affine/ext-loader/vitest.config.ts

@@ -8,7 +8,7 @@ export default defineConfig({
     include: ['src/__tests__/**/*.unit.spec.ts'],
     testTimeout: 500,
     coverage: {
-      provider: 'istanbul', // or 'c8'
+      provider: 'istanbul',
       reporter: ['lcov'],
       reportsDirectory: '../../../.coverage/ext-loader',
     },