feat: add footer statistics tracking with LangChain callbacks

- Add StatsCallbackHandler for tracking LLM calls, tool calls, and tokens
- Integrate callbacks into TradingAgentsGraph and all LLM clients
- Dynamic agent/report counts based on selected analysts
- Fix report completion counting (tied to agent completion)

tradingagents/graph/propagation.py

@@ -1,6 +1,6 @@
 # TradingAgents/graph/propagation.py
 
-from typing import Dict, Any
+from typing import Dict, Any, List, Optional
 from tradingagents.agents.utils.agent_states import (
     AgentState,
     InvestDebateState,
@@ -41,9 +41,17 @@ class Propagator:
             "news_report": "",
         }
 
-    def get_graph_args(self) -> Dict[str, Any]:
-        """Get arguments for the graph invocation."""
+    def get_graph_args(self, callbacks: Optional[List] = None) -> Dict[str, Any]:
+        """Get arguments for the graph invocation.
+
+        Args:
+            callbacks: Optional list of callback handlers for tool execution tracking.
+                       Note: LLM callbacks are handled separately via LLM constructor.
+        """
+        config = {"recursion_limit": self.max_recur_limit}
+        if callbacks:
+            config["callbacks"] = callbacks
         return {
             "stream_mode": "values",
-            "config": {"recursion_limit": self.max_recur_limit},
+            "config": config,
         }