User callback and sc_opf renaming

[SanjayJohnson02]

Added user callback capability, renamed scopf_model -> goc3_model

[sshin23]

We need testing for user extension

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.80%. Comparing base (563c722) to head (21067c2).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main      #24       +/-   ##
===========================================
+ Coverage   22.87%   88.80%   +65.93%     
===========================================
  Files           8        8               
  Lines        1303     1268       -35     
===========================================
+ Hits          298     1126      +828     
+ Misses       1005      142      -863     

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