Fix model pointer passed to callbacks

[odow]

This was changed in #143. But the change from ptr_model to model seems unintentional.

Based on the docstrings, it seems like it should be the pointer. It might be different to the one in model.

cc @frapac

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (a72f2a9) 84.53% compared to head (1281372) 84.53%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #277   +/-   ##
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  Coverage   84.53%   84.53%           
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  Files           3        3           
  Lines         996      996           
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  Hits          842      842           
  Misses        154      154           

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[frapac]

This looks good to me. As far as I remember, we were passing model before to pass (implicitly) some user data. This is no longer the case as we can pass directly model.ms_process_user_data and model.mip_node_user_data now.

[odow]

Yeah it seems like this is even a bug fix, because you'd be querying information from the base model, not from the current node that is being processed.