chore: setup vitest and example test

Author: sarod

browser-extension/package.json

@@ -16,7 +16,8 @@
     "lint": "eslint .",
     "lint:fix": "eslint --fix .",
     "format": "prettier --write .",
-    "format:check": "prettier --check ."
+    "format:check": "prettier --check .",
+    "test": "vitest"
   },
   "dependencies": {
     "image-js": "^1.3.0",
@@ -41,6 +42,7 @@
     "prettier": "^3.7.4",
     "typescript": "^5.9.3",
     "typescript-eslint": "^8.52.0",
+    "vitest": "^4.0.18",
     "wxt": "^0.20.13"
   },
   "pnpm": {