Optimize TestSuite comparison macro compile times.

[mosra]

I regularly get angry at how long large tests take to compile. Well, I guess relatively, building a heavy 6000-line GltfImporterTest.cpp in under 5 seconds is an unachievable feat in Some Other Codebases. But still.

Profiling using Clang -ftime-trace, the biggest offenders are:

• parsing the <sstream> include, about 160 ms / 3.5% -- depends on making Debug stream-free, which depends on ... making my own float printers
• parsing <cmath>, about 40 ms / 1% -- can't really do much about this, and the more I optimize, the more this will stand out
• template instantiations, about 1000 ms / 20%, of which the biggest chunks are:
  • TestSuite::Compare::Container<T>::printMessage(), about 500 ms / 10% -- put it into a non-templated base. These are not so many but quite large.
    • The comparator also does the comparisons twice on error, which is fine at runtime but adds even more pain to compile times. Why not just remember the first different item instead, instead of looping through everything again?!
  • TestSuite::Comparator<T>::printMessage() -- put it into a non-templated base. These are tiny but quite many, so the template base might not help as much.

Comparison with SpeedScope after adding a non-templated base for both Comparator and Compare::Container is above -- 4.9 seconds before, 4.5 after, time spent in printMessage() visibly shrinks. Trace files for reference:

• GltfImporterTest.cpp.original.zip
• GltfImporterTest.cpp.non-templated-base.zip

10% reduction in compile time is still not as significant as I hoped, further investigation needed:

• The actual container operator<<() seems to be quite heavy, anything to optimize there?
• What else?

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.40%. Comparing base (c5102b3) to head (468afdb).
⚠️ Report is 1258 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #140   +/-   ##
=======================================
  Coverage   98.40%   98.40%           
=======================================
  Files         124      125    +1     
  Lines        9504     9541   +37     
=======================================
+ Hits         9352     9389   +37     
  Misses        152      152           

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