optimized yfin fetching to be much faster

test.py

@@ -0,0 +1,11 @@
+import time
+from tradingagents.dataflows.y_finance import get_YFin_data_online, get_stock_stats_indicators_window, get_balance_sheet as get_yfinance_balance_sheet, get_cashflow as get_yfinance_cashflow, get_income_statement as get_yfinance_income_statement, get_insider_transactions as get_yfinance_insider_transactions
+
+print("Testing optimized implementation with 30-day lookback:")
+start_time = time.time()
+result = get_stock_stats_indicators_window("AAPL", "macd", "2024-11-01", 30)
+end_time = time.time()
+
+print(f"Execution time: {end_time - start_time:.2f} seconds")
+print(f"Result length: {len(result)} characters")
+print(result)