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/utils/package.json

@@ -6,7 +6,9 @@
   },
   "license": "MIT",
   "scripts": {
-    "lint": "eslint \"**/*.ts\""
+    "lint": "eslint \"**/*.ts\"",
+    "test": "vitest run",
+    "test:watch": "vitest --watch"
   },
   "dependencies": {
     "crypto-js": "^4.2.0",
@@ -17,6 +19,7 @@
     "@repo/typescript-config": "workspace:*",
     "@types/crypto-js": "^4.2.2",
     "eslint": "^8.57.1",
-    "typescript": "5.5.4"
+    "typescript": "5.5.4",
+    "vitest": "^4.0.17"
   }
 }