ant: replace usb.GetDevice with direct gousb usage
Remove dependency on antgo/driver/usb to fix libusb context leaks on
device-not-found errors. The previous code called usb.GetDevice which
creates a gousb.Context via libusb_init but leaks it on every error
path (device not found, interface claim failure, etc.). Calling
ListenForTrainer repeatedly (e.g. starting with no dongle and plugging
it in later) triggered a libusb assertion in pthread_key_create because
the leaked contexts were never torn down.
Replace with direct gousb calls in ListenForTrainer, managing the
gousb.Context lifecycle explicitly. Cleanup is ordered correctly on
all paths: release interface, close device, close context, cancel
the ANT message goroutine context.
Also convert panics to returned errors for graceful retry.
erik
9efdfc9b83