Fix bug in ProcessingIterator where it would run the tasks in only one single thread instead of using the pool

code/libraries/blocking-thread-pool/src/main/java/nu/marginalia/util/ProcessingIterator.java

@@ -38,7 +38,7 @@ public class ProcessingIterator<T> implements Iterator<T> {
 
     private void executeJob(ProcessingJob<T> job) {
         try {
-            job.run(this::executeTask);
+            job.run(j -> executorService.submit(() -> executeTask(j)));
         } catch (Exception e) {
             logger.warn("Exception while processing", e);
         } finally {