chore(atomic): migrate unit tests to vitest/browser (#4865)

https://coveord.atlassian.net/browse/KIT-3863

Following this example PR : #4858. 

This PR migrates most of the tests in atomic to the new solution we will
be using for unit testing in atomic :

Vitest Browser runs our tests in a browser and enables simple ES module
mocking. You will see it also opens up a UI when you run `npm run test`
in atomic !!

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Co-authored-by: GitHub Actions Bot <>

.github/workflows/prbot.yml

@@ -99,6 +99,8 @@ jobs:
 
       - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4
       - uses: ./.github/actions/setup
+      - name: Install Playwright Browsers
+        run: npx playwright install --with-deps
       - run: npm test
   package-compatibility:
     name: 'Verify compatibility of packages'