debug: add DNS verification and disable Java DNS caching

Troubleshooting 'seaweedfs-volume: Temporary failure in name resolution':

docker-compose.yml changes:
- Add MAVEN_OPTS to disable Java DNS caching (ttl=0)
  Java caches DNS lookups which can cause stale results
- Add ping tests before mvn test to verify DNS resolution
  Tests: ping -c 1 seaweedfs-volume && ping -c 1 seaweedfs-filer
- This will show if DNS works before tests run

workflow changes:
- List Docker networks before running tests
- Shows network configuration for debugging
- Helps verify spark-tests joins correct network

If ping succeeds but tests fail, it's a Java/Maven DNS issue.
If ping fails, it's a Docker networking configuration issue.

Note: Previous test failures may be from old code before Docker networking fix.

.github/workflows/spark-integration-tests.yml

@@ -189,6 +189,9 @@ jobs:
       working-directory: test/java/spark
       run: |
         echo "Running Spark integration tests in Docker container..."
+        echo "Docker networks:"
+        docker network ls
+        echo "Starting spark-tests container (will start dependencies automatically)..."
         docker compose up --abort-on-container-exit --exit-code-from spark-tests spark-tests
         echo "✓ Tests completed"