[ironrdp-rdpeusb] Client-side protocol state machine

[CBenoit]

Implement the client-side RDPEUSB protocol logic in ironrdp-rdpeusb. The client holds the physical USB device and responds to the server's IO requests.

Depends on:

• [ironrdp-dvc] Support multiple DVC channel instances with the same name #1135
• [ironrdp-rdpeusb] PDU encoding/decoding #1136

Tasks

• UrbdrcListener: implements DvcChannelListener; produces either a control channel or device channel processor depending on whether this is the first instance of "URBDRC" for the session
• UrbdrcControlChannel: implements DvcClientProcessor
• On start(): sends CHANNEL_CREATED, then RIM_EXCHANGE_CAPABILITY_REQUEST response
• On ADD_VIRTUAL_CHANNEL received: calls into the registered UsbClientBackend to detect available devices; queues device channel creation (surfaces via the listener factory on the next DYNVC_CREATE_REQ)
• UsbDeviceChannel: implements DvcClientProcessor
• On start(): sends CHANNEL_CREATED, then ADD_DEVICE
• Dispatches incoming server requests (IO_CONTROL, TRANSFER_IN_REQUEST, etc.) to UsbClientBackend
• Returns completions (URB_COMPLETION, IOCONTROL_COMPLETION) as DvcMessage
• On CANCEL_REQUEST: forwards cancellation to backend
• On RETRACT_DEVICE / channel close: teardown

Acceptance criteria

• Successful channel setup sequence (control channel up, capability exchange done)
• Successful new device sequence (device channel up, ADD_DEVICE sent)
• IO request dispatched to backend and completion returned correctly
• Protocol-level unit tests with mock backend