Feat: Make CityGmlArchive serializable

CityDoctorParent/Extensions/CityDoctorZipLoader/src/main/java/de/hft/stuttgart/citydoctor2/ziploader/CityGmlArchive.java

@@ -10,6 +10,7 @@ import java.io.FileInputStream;
 import java.io.IOException;
 import java.io.Serial;
 
+import java.io.Serializable;
 import java.nio.file.Path;
 import java.util.ArrayList;
 import java.util.List;
@@ -18,7 +19,7 @@ import java.util.zip.ZipEntry;
 import java.util.zip.ZipFile;
 import java.util.zip.ZipInputStream;
 
-public class CityGmlArchive {
+public class CityGmlArchive implements Serializable {
 
     private static final Logger logger = LogManager.getLogger(CityGmlArchive.class);