MNT speedup narx grad

[MatthewSZhang]

Checklist

• Used a personal fork to propose changes
• A reference to a related issue: MNT speedup NARX grad by Cython #156
• A description of the changes

1. rewrite _update_dydx and _predict in Cython
2. add profile task for narx

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (55d9e06) to head (229acc6).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #157   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            9         9           
  Lines          647       599   -48     
=========================================
- Hits           647       599   -48     

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