Fix CPU overhead in LLM Obs eval processor (#9765)

* fix MLOS-268

* change poll timeout to 100ms

Author: XG-xin

dd-java-agent/agent-llmobs/src/main/java/datadog/trace/llmobs/EvalProcessingWorker.java

@@ -145,7 +145,11 @@ public void run() {
     private void runDutyCycle() throws InterruptedException {
       Thread thread = Thread.currentThread();
       while (!thread.isInterrupted()) {
-        consumeBatch();
+        LLMObsEval eval = queue.poll(100, TimeUnit.MILLISECONDS);
+        if (eval != null) {
+          buffer.add(eval);
+          consumeBatch();
+        }
         flushIfNecessary();
       }
     }