Add LUQ (Long-text Uncertainty Quantification) scorer

[dylanbouchard]

Is your feature request related to a problem? Please describe.
We would like to incorporate the LUQ (Longform Uncertainty Quantification) scorer proposed by Zhang et al., 2024. While our current NLI-based scorers (Semantic Negentropy and Non-contradiction probability) are highly effective, their performance may be less effective on very long responses.

Describe the solution you'd like
To include the LUQ scorers, we would should include this in the NLIScorer class and offer it in the BlackBoxUQ scorer list.

Additional context
Note: Please do not ask to work on this issue unless you have read and fully understand the paper linked above.

[dylanbouchard]

Assigned to @virenbajaj