test: test on windows

[tlambert03]

This PR adds windows to the test matrix, and updates setup.py slightly to successfully build with pip install . on windows (provided you're in an environment with all the necessary deps)

[tlambert03]

currently failing to build, unable to find the scip headers... which is strange, since if I manually download the scip package the headers do appear to exist at an included dir: C:\Miniconda\envs\test\Include\...

"C:\Program Files\Microsoft Visual Studio\2022\Enterprise\VC\Tools\MSVC\14.34.31933\bin\HostX86\x64\cl.exe" /c 
/nologo /O2 /W3 /GL /DNDEBUG /MD -I.\ilpy -Iilpy/impl -IC:\Miniconda\envs\test\include 
-IC:\Miniconda\envs\test\Include 
"-IC:\Program Files\Microsoft Visual Studio\2022\Enterprise\VC\Tools\MSVC\14.34.31933\include" 
"-IC:\Program Files\Microsoft Visual Studio\2022\Enterprise\VC\Tools\MSVC\14.34.31933\ATLMFC\include" 
"-IC:\Program Files\Microsoft Visual Studio\2022\Enterprise\VC\Auxiliary\VS\include"
"-IC:\Program Files (x86)\Windows Kits\10\include\10.0.22621.0\ucrt" 
"-IC:\Program Files (x86)\Windows Kits\10\\include\10.0.22621.0\\um" 
"-IC:\Program Files (x86)\Windows Kits\10\\include\10.0.22621.0\\shared" 
"-IC:\Program Files (x86)\Windows Kits\10\\include\10.0.22621.0\\winrt" 
"-IC:\Program Files (x86)\Windows Kits\10\\include\10.0.22621.0\\cppwinrt" 
"-IC:\Program Files (x86)\Windows Kits\NETFXSDK\4.8\include\um" 
/EHsc /Tpilpy/wrapper.cpp /FoC:\Users\RUNNER~1\AppData\Local\Temp\tmpt6s7qhi7.build-temp\Release\ilpy/wrapper.obj -O3 -std=c++11 -DHAVE_SCIP -DHAVE_GUROBI


D:\a\ilpy\ilpy\ilpy\impl/solvers/ScipBackend.cpp(7): fatal error C1083: Cannot open include file: 'scip/scipdefplugins.h': No such file or directory