Add discover_printer(), _mac_of(), _port_open(), _sweep_arp(), _cache_ip()
with PRINTER_MAC/PRINTER_SUBNET/CACHE_FILE config + unit tests. Also adds
conftest.py to work around broken symlink that blocked pytest collection.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Mortdecai