FEAT add param fit_intercept for NARX

[MatthewSZhang]

Checklist

• Used a personal fork to propose changes
• A reference to a related issue: FEAT add fit_intercept support for NARX #77
• A description of the changes: add fit_intercept argument for NARX

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (84b2f83) to head (3aecd2b).
Report is 11 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #78   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            6         6           
  Lines          603       604    +1     
=========================================
+ Hits           603       604    +1     

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