FIX minibatch ssc score not match gtruth

[MatthewSZhang]

Checklist

• Used a personal fork to propose changes
• A reference to a related issue: BUG ssc score of minibatch not match ground truth #199
• A description of the changes:

1. normalize target y to fix the bug
2. add unit test to check if ssc of minibatch match ground truth

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (5c2dbe3) to head (6906991).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #200   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           10        10           
  Lines          681       687    +6     
=========================================
+ Hits           681       687    +6     

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