chore: upgrade Vitest to v4.0.13 and add browser testing support

- Upgrade Vitest from 2.1.5 to 4.0.13 and related packages (@vitest/coverage-v8, @vitest/ui)
- Add @vitest/browser-playwright for browser-based testing capabilities
- Add new test:browser npm script for running browser tests
- Update pnpm lockfile with new dependencies and Rollup platform binaries

Author: JannikZed

package.json

@@ -18,7 +18,8 @@
     "test:ui": "vitest --ui  --config vite.config.ts",
     "test:unit": "vitest --config vite.config.ts src/**/*.test.ts src/**/*.test.tsx",
     "test:integration": "vitest --config vite.config.ts ./test/integration/nextjs-cache-handler.integration.test.ts",
-    "prepare": "./scripts/prepare.sh"
+    "prepare": "./scripts/prepare.sh",
+    "test:browser": "vitest --config=vitest.browser.config.ts"
   },
   "main": "dist/index.js",
   "module": "dist/index.mjs",
@@ -74,8 +75,9 @@
     "@semantic-release/npm": "^12.0.1",
     "@typescript-eslint/eslint-plugin": "^8.15.0",
     "@typescript-eslint/parser": "^8.15.0",
-    "@vitest/coverage-v8": "^2.1.5",
-    "@vitest/ui": "^2.1.5",
+    "@vitest/browser-playwright": "^4.0.13",
+    "@vitest/coverage-v8": "^4.0.13",
+    "@vitest/ui": "^4.0.13",
     "eslint": "^9.15.0",
     "lint-staged": "^15.2.10",
     "node-fetch": "3",
@@ -84,7 +86,7 @@
     "semantic-release": "^24.2.0",
     "tsup": "^8.4.0",
     "typescript": "^5.6.3",
-    "vitest": "^2.1.5"
+    "vitest": "^4.0.13"
   },
   "peerDependencies": {
     "next": ">=15.0.3 <= 15.4.7",