test: enable Windows python suite

[MukundaKatta]

Summary

• add windows-latest to the Python test-suite workflow matrix
• skip the signal.alarm-based big-file timeout test on platforms that do not expose SIGALRM
• keep the slow-file timeout coverage on Unix-like platforms while unblocking Windows CI for the rest of the suite

Fixes #789

Validation

• compiled python/tests/test_magika_python_module.py successfully with python3 -m py_compile
• attempted to run the targeted test locally, but this clone does not have onnxruntime installed, so full runtime execution was not available here