Add helper method for genai metrics

[kartikc727]

Added a helper method get_genai_metric_mean to return the mean of the metrics calculated for individual data points.

Updated the test for genai metrics to also test for this new helper method, and refactored some repeated code into a helper function.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (7aa72fb) 88.24% compared to head (eeefe71) 80.91%.

❗ Current head eeefe71 differs from pull request most recent head 008060f. Consider uploading reports for the commit 008060f to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2519      +/-   ##
==========================================
- Coverage   88.24%   80.91%   -7.34%     
==========================================
  Files         142       34     -108     
  Lines        7952     2483    -5469     
==========================================
- Hits         7017     2009    -5008     
+ Misses        935      474     -461     

Flag	Coverage Δ
unittests	80.91% <100.00%> (-7.34%)	⬇️

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