feat(vitest-plugin): add vite 8 support

Add vite ^8.0.0 to the peer dependency range and bump the dev
dependency to test against the latest. Vite 8 replaces esbuild/Rollup
with Rolldown, which changes the Plugin type's inheritance chain.
Add rolldown as a dev dependency so pnpm can resolve the transitive
types needed for the build.

Co-Authored-By: Claude <noreply@anthropic.com>

Author: adriencaccia

packages/vitest-plugin/package.json

@@ -32,14 +32,15 @@
   },
   "peerDependencies": {
     "tinybench": ">=2.9.0",
-    "vite": "^4.2.0 || ^5.0.0 || ^6.0.0 || ^7.0.0",
+    "vite": "^4.2.0 || ^5.0.0 || ^6.0.0 || ^7.0.0 || ^8.0.0",
     "vitest": "^3.2 || ^4"
   },
   "devDependencies": {
     "@total-typescript/shoehorn": "^0.1.1",
     "execa": "^8.0.1",
+    "rolldown": "1.0.0-rc.11",
     "tinybench": "^2.9.0",
-    "vite": "^7.0.0",
+    "vite": "^8.0.0",
     "vitest": "^4.0.18"
   }
 }