Use decorator for "register_auto_reply"

[BeibinLi]

Use decorator to simply the auto reply function registration.

Why are these changes needed?

Related issue number

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• I've added tests (if relevant) corresponding to the changes introduced in this PR.
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[sonichi]

Thanks for making the registration more convenient. Could you also modify the chess notebook?
Also, could you add a test for a class inheriting two subclasses of ResponsiveAgent and make the registration works as expected?

[BeibinLi]

Thanks for making the registration more convenient. Could you also modify the chess notebook? Also, could you add a test for a class inheriting two subclasses of ResponsiveAgent and make the registration works as expected?

Test cases added and suggestions resolved.

TODO:

• Handle the Chess example.