feat(tests): add basic arithmetic functions and corresponding tests

- Implemented `add` and `subtract` functions in multiple packages (web, ui, utils).
- Created unit tests for these functions using Vitest in respective test files.
- Updated turbo.json to include a new test pipeline for coverage and watch mode.

packages/ui/package.json

@@ -7,11 +7,13 @@
   },
   "license": "MIT",
   "scripts": {
-    "lint": "eslint \"**/*.ts\""
+    "lint": "eslint \"**/*.ts\"",
+    "test": "vitest run",
+    "test:watch": "vitest --watch"
   },
   "dependencies": {
-    "@tailwindcss/vite": "^4.1.18",
     "@repo/utils": "workspace:*",
+    "@tailwindcss/vite": "^4.1.18",
     "react": "^19.2.3",
     "react-dom": "^19.2.3",
     "tailwind-merge": "^3.4.0",
@@ -26,6 +28,7 @@
     "@vitejs/plugin-react": "^5.1.2",
     "eslint": "^8.57.1",
     "typescript": "5.5.4",
-    "vite": "^5.1.4"
+    "vite": "^5.1.4",
+    "vitest": "^4.0.17"
   }
 }