Add timeout support for IIS search

[haman80]

Add timeout support to getIIS

• Introduced a new iis_time_limit option to distinguish IIS search limits from the time_limit option
• Updated deletion filtering to return a partial IIS when the time limit is reached
• Added new model status kIisModelStatusTimeLimit

Improve handling of unexpected model statuses

• Temporarily modify options that may interfere with IIS search, including: simplex_iteration_limit, objective_bound, allow_unbounded_or_infeasible, Callbacks
• Updated getIisInterface to first establish infeasibility prior to elastic filtering or deletion filtering; abort IIS computation if the model is not confirmed infeasible
• After confirming infeasibility, attempt elastic filtering if requested; if it fails due to an unknown status, fall back to deletion filtering over the full set of row and column bounds
• Enhanced deletion filtering to skip bounds whose removal results in an unknown model status and return a partial IIS if possible

Enhancements to HighsIis

• Extended HighsIisInfo to track min, max, and mean iteration counts and LP solve times
• Centralize responsibility for updating these metrics
• Added helper methods determineBoundStatus, and processBoundRelaxation to reduce duplicated logic and improve maintainability

[jajhall]

@haman80 I've cleared the merge conflicts and pushed to Git

[codecov]

Codecov Report

❌ Patch coverage is 87.31563% with 43 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.87%. Comparing base (c1a8ebe) to head (9dcfccb).
⚠️ Report is 32 commits behind head on latest.

Files with missing lines	Patch %	Lines
highs/lp_data/HighsInterface.cpp	77.77%	32 Missing ⚠️
highs/lp_data/HighsIis.cpp	88.23%	10 Missing ⚠️
highs/lp_data/HighsOptions.h	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           latest    #2870      +/-   ##
==========================================
+ Coverage   80.65%   80.87%   +0.21%     
==========================================
  Files         347      347              
  Lines       86690    86824     +134     
==========================================
+ Hits        69920    70216     +296     
+ Misses      16770    16608     -162     

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[haman80]

Hi @jajhall ,
Apologies for the additional commits. I added some unit tests to improve coverage, including a couple of new infeasible LP instances (cplex1 and vol1). The vol1 case was initially exhibiting inconsistent behavior across machines due to ill conditioning, which required some iteration to stabilize. I look forward to hearing your thoughts.

[jajhall]

Other than the one error you inherited from me - see comment - this is largely OK.

I'll compile and run it to study it further

[jajhall]

Partly to understand the flow of your modified code, I've added a couple more unit tests to TestIis.cpp. These expose a few minor issues (tagged with "fix-2870") that need resolving

[haman80]

Partly to understand the flow of your modified code, I've added a couple more unit tests to TestIis.cpp. These expose a few minor issues (tagged with "fix-2870") that need resolving

@jajhall Thank you so much for the review. I pushed another commit addressing the issues tagged with "fix-2870". Please feel free to take a look and let me know your thoughts.

[jajhall]

This addresses my original request for changes, so is good to be merged once the CI tests pass.

[haman80]

This addresses my original request for changes, so is good to be merged once the CI tests pass.

@jajhall Thanks again for the review. I fixed the CI failure, which was due to a format-type mismatch in reportIisInfo in TestIis.cpp (passing int to %g instead of double). I will go ahead and merge.