Bluetooth B2: HCI scheme daemon and HciBackend transport bridge
Add scheme.rs to btusb daemon serving scheme:hciN with full SchemeSync
implementation (status, info, command, events, ACL, LE scan/connect/
disconnect). Add hci_backend.rs to btctl implementing Backend trait via
scheme filesystem reads/writes instead of stub data. Backend selection
via REDBEAR_BTCTL_BACKEND=hci env var, StubBackend remains default.
Fix daemon_main to use correct redox-scheme 0.11 API (Socket::create,
next_request/handle_sync/write_response loop) instead of non-existent
SchemeBlock.
125 btusb tests, 45 btctl tests, 2 wifictl tests passing.
vasilito
8ff8c084f5