Refactor HighsRedcostFixing::addRootRedcost

[fwesselm]

• This PR is a by-product of debugging and removes duplicate code from HighsRedcostFixing::addRootRedcost().
• The new code behaves slightly different due to the fact that the lower bound check now uses a tolerance for both directions (i.e., mipsolver.mipdata_->lower_bound + mipsolver.mipdata_->feastol).
• I ran 850+ MIPs and the relative geometric means for solution times and numbers of branching nodes are 0.99 and 1.01 respectively, indicating that the impact on HiGHS' performance is very small.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.24%. Comparing base (e4632db) to head (dbe2d8a).
⚠️ Report is 64 commits behind head on latest.

Additional details and impacted files

@@            Coverage Diff             @@
##           latest    #2660      +/-   ##
==========================================
+ Coverage   81.20%   81.24%   +0.03%     
==========================================
  Files         349      349              
  Lines       85465    85767     +302     
==========================================
+ Hits        69406    69681     +275     
- Misses      16059    16086      +27     

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[Opt-Mucca]

What do you mean by the second point? Isn't lower_bound already accounting for feastol? From what I understood you're now doubling the tolerance in your check.

[fwesselm]

What do you mean by the second point? Isn't lower_bound already accounting for feastol? From what I understood you're now doubling the tolerance in your check.

Thanks for checking the code. I do not think lower_bound includes a tolerance. I was trying to explain that the former if-part did not use a tolerance when comparing lower_bound and cutoff bound while the else-part did.

[Opt-Mucca]

I'm blind. All good! The lower_bound in HighsPrimalHeuristics is not mipsolver->mipdata_.......