Feature(LLMLingua): add RetrievalAttention, SCBench

[iofu728]

What does this PR do?

• Add RetrievalAttention, SCBench;

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Was this discussed/approved via a Github issue? Please add a link
  to it if that's the case.
• Did you make sure to update the documentation with your changes?
• Did you write any new necessary tests?

Who can review?

@iofu728

[Copilot]

Copilot reviewed 1 out of 1 changed files in this pull request and generated no comments.