Fix: rectify bugs of not toggling the flag when an inner change occurs in a container

[Ahzyuan]

📋 Summary

Important

• This PR fixes a bug.
• This PR adds something new.
• This PR is not a code change (e.g. README, typos, ...)
• This PR has been tested.

📝 Changes

Details

• torchmeter/config.py:
  • add CallbackList and CallbackSet classes to spy the inner change of a list or a set.
  • fix the bug that config_file can not be reset to None.
  • change the config representation style: used a hierarchical structure and specific data types to make it clearer.