test: Add Vitest for testing and implement hmacSHA256Base64 tests

- Added Vitest as a development dependency for testing.
- Created a new test file for hmacSHA256Base64 utility function with two test cases:
  - Validates the base64 signature for known input.
  - Ensures different signatures are returned for different messages.

Author: c-c-epr

.github/workflows/check.yml

@@ -61,3 +61,22 @@ jobs:
 
       - name: Prettier format check
         run: npm run format:check
+
+  test:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v6
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v6
+        with:
+          node-version: 22
+          cache: npm
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Run unit tests
+        run: npm run test:run