Add enhancement options to useCopyCode and buttonClass

[tuyuritio]

This PR includes two improvements:

1. Added displayDuration option to the useCopyCode hook, allowing developers to customize the duration of the feedback message after copying.
2. Introduced a fallback mechanism for buttonClass to ensure it works correctly in decoupled frontend-backend environments.

[howcasperwhat]

Please run npm run lint --fix before commit to fix eslint code formatting problems. (See CONTRIBUTING.md - apologies, I hadn't made it clear in the guide that this step is required)

Thanks!

[tuyuritio]

Oh... I apologize for my series of improper actions. I think it should be fixed now.