Add "kappa proportion" metric

[tsalo]

Closes none. This is just an idea that might be useful.

Changes proposed in this pull request:

• Add "kappa proportion" metric defined as kappa / (kappa + rho).

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.32%. Comparing base (1151c90) to head (2d79396).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1355      +/-   ##
==========================================
+ Coverage   90.30%   90.32%   +0.01%     
==========================================
  Files          30       30              
  Lines        4726     4734       +8     
  Branches      790      792       +2     
==========================================
+ Hits         4268     4276       +8     
  Misses        309      309              
  Partials      149      149              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.