Various minor improvements to HiPO

[filikat]

• Adjust some variable names that were not following the naming convention.
• Simplify some of the internal interfaces between objects in HiPO.
• Simplify the timers that are switched on/off at compile time.
• Other various minor changes to make the code cleaner.
• Reorganize FactorHiGHSSolver.cpp and remove some redundant copies of matrix A.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.29%. Comparing base (b74fc43) to head (696cedb).
⚠️ Report is 55 commits behind head on latest.

Additional details and impacted files

@@           Coverage Diff           @@
##           latest    #2706   +/-   ##
=======================================
  Coverage   81.29%   81.29%           
=======================================
  Files         349      349           
  Lines       85786    85795    +9     
=======================================
+ Hits        69736    69746   +10     
+ Misses      16050    16049    -1     

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[filikat]

Closes #2683

[jajhall]

Great: this is maturing nicely