add print number of info_state

Author: kibitzing

examples/OpenEnv_Tutorial.ipynb

@@ -895,6 +895,7 @@
     "\n",
     "print(\"📥 Received OpenSpielObservation:\")\n",
     "print(f\"   • info_state: {result.observation.info_state[:10]}... (first 10 values)\")\n",
+    "print(f\"   • number of info_state: {len(result.observation.info_state)}\")\n",
     "print(f\"   • legal_actions: {result.observation.legal_actions}\")\n",
     "print(f\"   • game_phase: {result.observation.game_phase}\")\n",
     "print(f\"   • done: {result.done}\")\n",