feat: add IP & ICMP packet implementations (#14)

This PR adds new modules with IP and ICMP packet implementations, along
with jest integration to start adding unit tests.

.github/workflows/ci.yml

@@ -47,3 +47,20 @@ jobs:
 
       - name: Lint project
         run: npm run lint
+
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Use Node.js 20
+        uses: actions/setup-node@v4
+        with:
+          node-version: ${{ env.NODE_VERSION }}
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Lint project
+        run: npm run test