feat: Make BigQueryAgentAnalyticsPlugin state per-invocation

This change introduces per-invocation instances of BatchProcessor and TraceManager, managed by ConcurrentHashMaps keyed by invocation ID. This ensures that analytics and tracing data are isolated for each concurrent invocation. BatchProcessors and TraceManagers are created lazily on the first event for a given invocation and are cleaned up when the invocation completes.

PiperOrigin-RevId: 897370846

Author: google-genai-bot

core/src/main/java/com/google/adk/plugins/agentanalytics/BatchProcessor.java

@@ -249,7 +249,7 @@ private void populateVector(FieldVector vector, int index, Object value) {
 
   @Override
   public void close() {
-    if (this.queue != null && !this.queue.isEmpty()) {
+    while (this.queue != null && !this.queue.isEmpty()) {
       this.flush();
     }
     if (this.allocator != null) {