Function spawn 

pub fn spawn(
    home: UnifierHome,
    store: Arc<Mutex<HotStore>>,
    shutdown: Arc<AtomicBool>,
    http_activity: Arc<AtomicBool>,
) -> Result<u16>

Spawn the localhost HTTP listener. Returns the bound port. http_activity is set true on each accepted request so the daemon idle timer stays fresh while browsers are hitting temp reports.