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.

package.json

@@ -8,10 +8,10 @@
     "dev:web": "turbo run dev --filter=web",
     "dev:docs-dev": "turbo run dev --filter=docs-dev",
     "lint": "turbo run lint",
-    "format": "prettier --write \"**/*.{ts,tsx,md}\""
+    "format": "prettier --write \"**/*.{ts,tsx,md}\"",
+    "test": "turbo run test"
   },
   "devDependencies": {
-    "eslint": "^8.57.0",
     "prettier": "^3.2.5",
     "turbo": "^2.7.2"
   },