Update tools.py

SyntaxError: f-string expression - line 185

tools.py

@@ -182,5 +182,5 @@ if __name__ == "__main__":
     # Test Python REPL Tool
     print("\n--- Python REPL Tool Test ---")
     print(f"Python REPL '2 + 2': {python_repl_tool.invoke({'code': '2 + 2'})}")
-    print(f"Python REPL 'len(\"hello\")': {python_repl_tool.invoke({'code': 'len(\"hello\")'})}")
+    print(f"Python REPL 'len(\'hello\')': {python_repl_tool.invoke({'code': 'len(\'hello\')'})}")
     print(f"Python REPL error: {python_repl_tool.invoke({'code': '10 / 0'})}")