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/configs/eslint/package.json

@@ -3,6 +3,7 @@
   "version": "0.0.0",
   "license": "MIT",
   "files": [
+    "index.js",
     "library.js",
     "react.js",
     "storybook.js"