Add pool.finalize() call after building trajectory pool for O(1) sampling

trainer.py

@@ -74,6 +74,9 @@ class NSGFTrainer:
             if (batch_idx + 1) % max(1, num_batches // 10) == 0:
                 logger.info(f"  Pool building: {batch_idx + 1}/{num_batches}, pool size: {len(self.pool)}")
         logger.info(f"Trajectory pool built. Total entries: {len(self.pool)}")
+        # Pre-concatenate for O(1) sampling during training
+        self.pool.finalize()
+        logger.info("Trajectory pool finalized (pre-concatenated for fast sampling).")
 
     def train(self) -> Dict[str, list]:
         self.model.train()