TypedPython: cl.exe output decoded as UTF-8 raises UnicodeDecodeError on Korean Windows #350

On Korean Windows, typedpython demo prints a UnicodeDecodeError traceback from subprocess's reader thread: cl.exe writes in the console code page (CP949), and CPython 3.15 decodes text=True output as UTF-8. The build still succeeds, but a compile error message would be lost.

Fix: decode cl.exe and vswhere output with the OEM code page and errors="replace".

Done when: test_cbuild_msvc.py passes and the demo on Korean Windows prints no traceback.