Have cibuildwheel use `TestPythonSML.py` for test command

[ShadowJonathan]

After #448

Currently this following python code is executed to test:

import soar_sml

k = soar_sml.Kernel.CreateKernelInNewThread()
a = k.CreateAgent('soar')

assert(a.ExecuteCommandLine('echo hello world').strip() == 'hello world')

This makes sure the library at least imports, and the kernel can start, but it doesn't do a deeper test of the library itself.

We could (re)use TestPythonSML.py for this, and run it for every single wheel. This'll increase build times, but it could be a more thorough check of what we send to pypi.

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Currently there are two lines / chunks which need to be properly converted before we can change the test command to python TestPythonSML.py;

• This import line needs to fallback to using soar_sml, if this is installed that way.

• This path-determining line needs to be replaced if soar_sml is imported, since then the file is installed in an installation directory.
  Instead, we should probably either look at an environment variable, or simply assume the current directory, or possibly walk up directory parents until we see SoarUnitTests