Split tests into a few different files

[rayegun]

I'm not very happy with these splits, but they're all relatively small files, and have some logic to them.

This will be followed by a complete test re-org at some point. For now we're just aiming to reduce the sizes of each test file.

If there's a better split just let me know and I'll change it!

[codecov-commenter]

Codecov Report

Merging #151 (b9cb1b4) into main (4ca114b) will decrease coverage by 0.59%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #151      +/-   ##
==========================================
- Coverage   34.23%   33.64%   -0.60%     
==========================================
  Files          25       25              
  Lines       21121    21121              
==========================================
- Hits         7231     7106     -125     
- Misses      13890    14015     +125     

Impacted Files	Coverage Δ
src/solvers/lib/i686-w64-mingw32.jl	0.00% <0.00%> (-12.38%)	⬇️
src/sparsematrix.jl	95.28% <0.00%> (-0.05%)	⬇️

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[ViralBShah]

In the future, it would be better to make branches in this repo than forks since that would then allow others who have commit access to directly add to the branch.

[ViralBShah]

One more thing that is useful is to move the USE_GPL_LIBS check to the individual solver files instead of having it in runtests.jl, and perhaps put all of them in the same directory - so that they can be added to testgroups. That way even those will run in parallel across workers.

[ViralBShah]

Figured it's easier to merge and do another PR for the solvers.

[rayegun]

Oh that's why everyone has their own branches. Good to know!