Added Highs::closeLogFile(), and calling this before returning from the command line executable

[jajhall]

This ensures that the log file is closed, but surely that happens in the destructor of the Highs class.

Hence I'm puzzled by the issue raised in #2534

Still Highs::closeLogFile() may be useful to someone, and now there's an explicit flush of Highs::options_.log_options.log_stream in the destructor.

[codecov]

Codecov Report

❌ Patch coverage is 65.62500% with 11 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.70%. Comparing base (b9cee31) to head (2e5d7eb).
⚠️ Report is 26 commits behind head on latest.

Files with missing lines	Patch %	Lines
app/RunHighs.cpp	42.10%	11 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           latest    #2558      +/-   ##
==========================================
+ Coverage   79.66%   79.70%   +0.04%     
==========================================
  Files         346      346              
  Lines       86430    86427       -3     
==========================================
+ Hits        68854    68889      +35     
+ Misses      17576    17538      -38     

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[galabovaa]

Looks good to me!