Support all ObjSCIP features

[hedtke]

Closes #29

Adds support for all ObjSCIP features.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.63%. Comparing base (44d6a47) to head (d402e29).
⚠️ Report is 2 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #44      +/-   ##
==========================================
+ Coverage   97.75%   99.63%   +1.87%     
==========================================
  Files          10       11       +1     
  Lines         223      274      +51     
  Branches       64       85      +21     
==========================================
+ Hits          218      273      +55     
+ Misses          4        0       -4     
  Partials        1        1              

Files with missing lines	Coverage Δ
include/scippp/model.hpp	100.00% <100.00%> (+3.70%)	⬆️
source/model.cpp	98.90% <100.00%> (+0.94%)	⬆️
source/model_objscip.cpp	100.00% <100.00%> (ø)

... and 4 files with indirect coverage changes