style: add BitsAndBytesConfig __repr__ function
Author: aarnphm
Pull request: yes

# What does this PR do?

Add a `__repr__` to `transformers.BitsAndBytesConfig` to make it nice to print.

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## Who can review?

cc @sgugger

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Comments:
_The documentation is not available anymore as the PR was closed or merged._

Hi @amyeroberts I have addressed all of the issue. PTAL when you are available. Thanks a bunch.

Can you rebase your branch on main? This should fix the failing test. Thanks!

done.

Thanks a lot for working on this @aarnphm ! Nice job!