Hold scipptr in variable to eliminate use-after-free errors

[mmghannam]

This is the last part of #152

[mmghannam]

@Andful would be great if you could take another look here, thanks again for your help!

[Andful]

Looks good. I personally would be stricter with unsafety. I would mark a function unsafe if there exists arguments that would cause UB, even if they are edge cases, e.g. NULL or dangling pointers.

[Andful]

See #159 (comment)

[mmghannam]

@Andful thanks a lot for the quick and helpful review! you caught a lot of potential issues.

[codecov]

Codecov Report

Attention: Patch coverage is 81.00000% with 19 lines in your changes missing coverage. Please review.

Project coverage is 76.12%. Comparing base (a7b9ef3) to head (b642e74).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/scip.rs	84.21%	9 Missing ⚠️
src/model.rs	58.82%	7 Missing ⚠️
src/variable.rs	75.00%	2 Missing ⚠️
src/branchrule.rs	94.44%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #160      +/-   ##
==========================================
- Coverage   76.23%   76.12%   -0.12%     
==========================================
  Files          13       13              
  Lines        1805     1859      +54     
==========================================
+ Hits         1376     1415      +39     
- Misses        429      444      +15     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.