TST add equivalence check for sample weights

[MatthewSZhang]

Checklist

• Used a personal fork to propose changes
• A reference to a related issue: TST test sample weight for NARX #67
• A description of the changes: use static narx model to check if the loss function correctly handle sample weights by equivalence test through repeating or removing samples

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (84b2f83) to head (340bc3c).
Report is 9 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #76   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
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  Files            6         6           
  Lines          603       585   -18     
=========================================
- Hits           603       585   -18     

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