FEAT add jac for narx

[MatthewSZhang]

Checklist

• Used a personal fork to propose changes
• A reference to a related issue: Add Jacobian matrix for multi-step-ahead narx loss #63
• A description of the changes
  Add Jacobian matrix for fitting NARX

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (d4306c4) to head (183d8cc).
Report is 59 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##              main       #66    +/-   ##
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  Coverage   100.00%   100.00%            
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  Files            3         6     +3     
  Lines          110       603   +493     
==========================================
+ Hits           110       603   +493     

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[MatthewSZhang]

Fix #69
Current MSA NARX optimisation is very sensitive to noise. We have to reduce the noise to make optimiser to find the optimum easier.

[MatthewSZhang]

Implement #68