feat(ci): add codecov workflow for test coverage reporting

Add GitHub Actions workflow to run tests with coverage and upload
results to Codecov. The workflow:
- Runs on push to main and pull requests
- Uses Go 1.23
- Executes make coverage with race detection enabled
- Uploads coverage.out to Codecov for tracking

Signed-off-by: Alejandro Mery <amery@apptly.co>

Author: amery

.github/workflows/codecov.yml

@@ -0,0 +1,31 @@
+name: Test and Coverage
+
+on:
+  push:
+    branches: [ main ]
+  pull_request:
+    branches: [ main ]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4
+
+    - name: Set up Go
+      uses: actions/setup-go@v5
+      with:
+        go-version: '1.23'
+
+    - name: Run tests with coverage
+      run: |
+        export GOTEST_FLAGS="-race -covermode=atomic"
+        make coverage
+
+    - name: Upload coverage to Codecov
+      uses: codecov/codecov-action@v5
+      with:
+        files: ./coverage.out
+        flags: unittests
+        name: codecov-core
+        fail_ci_if_error: true