Add Reciprocal Rank Fusion

[svilupp]

• Added a utility function to RAGTools reciprocal_rank_fusion, as a principled way to merge multiple rankings. See ?RAGTools.Experimental.reciprocal_rank_fusion for more information.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 91.98%. Comparing base (751f337) to head (c2e92ab).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #173 +/- ## ========================================== + Coverage 91.96% 91.98% +0.02% ========================================== Files 45 45 Lines 3744 3754 +10 ========================================== + Hits 3443 3453 +10 Misses 301 301 ```

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