Function start_station 

async fn start_station(device: Interface<'static>, spawner: Spawner) -> bool

Brings up the embassy-net stack on the station interface with a DHCP client and waits for the lease.

Returns false when no lease arrives within STA_DHCP_TIMEOUT so the caller can fall back to AP mode. The station stack is then abandoned: its runner idles safely (the driver refuses TX while the link is down) and never spawned HTTP sockets.