add bert score

[bugtig6351]

• add bert score
• fix answer extracting function in asqa benchmark
• add condition checks before nltk.download('punkt'), prevent the following message appearing every time rageval is run.

  [nltk_data] Downloading package punkt to data\nltk...
  [nltk_data]   Package punkt is already up-to-date!

[codecov[bot]]

Codecov Report

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

Project coverage is 81.45%. Comparing base (f75de18) to head (3e0f9b9).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #109 +/- ## ========================================== + Coverage 80.88% 81.45% +0.57% ========================================== Files 32 33 +1 Lines 1135 1170 +35 ========================================== + Hits 918 953 +35 Misses 217 217 ```

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