Decode Pi smoke-test output as UTF-8 on Windows #245

The Pi smoke check uses text-mode subprocess pipes without an explicit encoding. On Windows with a cp1252 locale, Pi emits UTF-8 RPC output containing bytes that raise UnicodeDecodeError in scripts/check_pi_extension.py. The smoke check then times out instead of reporting extension behavior. Please configure UTF-8 decoding for the Pi RPC and captured CLI output, with safe handling of malformed diagnostics.