Implements AsyncWorker — the daemon asyncio thread that owns the meshcore
library connection, subscribes to all relevant EventTypes, and feeds events
back into MeshcoreClient via on_message/on_node/on_telemetry/on_traceroute/
on_connected/on_error. Includes retry-with-backoff (3 attempts: 5s/15s/45s),
thread-safe send_text/request_traceroute/scan_ble_sync for Flask callers,
and a standalone _scan_ble() coroutine using bleak.BleakScanner.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
James Smith