Fix: Replace StrEnum with strenum in code_exec.py (#9376)

### What problem does this PR solve?

- The enum import was changed from Python's built-in StrEnum to the
strenum package.
- Fix error `Warning: Failed to import module code_exec: cannot import
name 'StrEnum' from 'enum' (/usr/lib/python3.10/enum.py)`

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

agent/tools/code_exec.py

 import logging
 import os
 from abc import ABC
-from enum import StrEnum
+from strenum import StrEnum
 from typing import Optional
 from pydantic import BaseModel, Field, field_validator
 from agent.tools.base import ToolParamBase, ToolBase, ToolMeta