add mathematical solver engine based on sympy

tool_helper.py

@@ -11,6 +11,7 @@ def tool(fn):
     """tool function decorator"""
     print("register tool '%s'" % fn.__name__)
     tool_list.append(fn)
+    return fn
 
 # def parse_and_execute_tool_call(message: str, tools: list[function]) -> str | None:
 #     """execute tool call if needed accordint <tool_call> tag and return the content of the tool call or None if no call happened."""