add codecov upload workflow

.github/workflows/coverage.yml

@@ -0,0 +1,31 @@
+name: coverage
+
+on:
+  pull_request:
+    branches:
+      - main
+  push:
+    branches:
+      - main
+
+jobs:
+  codecov:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version-file: .node-version
+          cache: npm
+
+      - run: npm ci
+
+      - name: Run tests
+        run: npx jest --coverage
+
+      - name: Upload results to Codecov
+        uses: codecov/codecov-action@v4
+        with:
+          token: ${{ secrets.CODECOV_TOKEN }}