Replace the stub probe with a real IOKit/IOUSBFamily transport:
discovery by VID/PID, device and interface connections, vendor
control requests on EP0, bulk writes to EP 0x04 OUT, and an async
read pump (EP 0x05 IN / EP 0x04 IN) on a dedicated CFRunLoop
thread with disconnect notification.
Add the test_usb suite, link IOKit/CoreFoundation into xone_usb,
and update the README investigation checklist.
Co-Authored-By: qwen3.8-27b@q2_k_xl: implemented USB transport layer
portersky
4f0f1ff75d