Add a simulated USB Audio Class 1 loopback device for testing
isochronous transfers. Audio sent to the playback OUT endpoint
(48kHz/16-bit/stereo) is looped back to the capture IN endpoint.
- Add UsbEndpoint::transfer_type() masking bmAttributes to bits 0-1,
fixing dispatch for isochronous endpoints with sync-type sub-bits
- Update all endpoint attribute dispatch sites across the library
- Add UacLoopbackBuffer, UacControlHandler, UacStreamOutHandler,
UacStreamInHandler in lib/src/uac.rs
- Add build_uac_loopback_device() builder function
- Add `test_uac connect` CLI subcommand
- Add 10 unit tests covering buffer, descriptors, and handler behavior
- Add design spec and implementation plan docs
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Davíð Steinn Geirsson
18a413870a