ci: add test coverage reporting to workflow

run tests with race detector and coverage profiling, upload results
to codecov for visibility into test coverage metrics

.github/workflows/go.yml

@@ -12,6 +12,13 @@ jobs:
       - name: Set up Go
         uses: actions/setup-go@v4
         with:
-          go-version: "1.23"
+          go-version: "1.24"
       - name: Build
         run: make
+      - name: Run tests with coverage
+        run: go test -race -coverprofile=coverage.out -covermode=atomic ./...
+      - name: Upload coverage to Codecov
+        uses: codecov/codecov-action@v4
+        with:
+          files: ./coverage.out
+          fail_ci_if_error: false