Fix null threadFactory in EventsTask when not configured

EventsTask now handles null threadFactory by using the default
Executors.newSingleThreadScheduledExecutor() without a factory argument.
This allows tests to run without configuring a thread factory in the SDK config.

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

AI-Session-Id: c83b3557-2c02-4d13-aaa4-273b7340163d
AI-Tool: claude-code
AI-Model: unknown

Author: gthea

tracker/src/main/java/io/split/client/events/EventsTask.java

@@ -38,7 +38,9 @@ public EventsTask(EventsStorageConsumer eventsStorageConsumer,
         _eventsStorageConsumer = Objects.requireNonNull(eventsStorageConsumer);
         _sendIntervalMillis = sendIntervalMillis;
         _eventsSender = Objects.requireNonNull(eventsSender);
-        _senderScheduledExecutorService = Executors.newSingleThreadScheduledExecutor(threadFactory);
+        _senderScheduledExecutorService = threadFactory != null
+                ? Executors.newSingleThreadScheduledExecutor(threadFactory)
+                : Executors.newSingleThreadScheduledExecutor();
     }
 
     public void start(){