Function serve 

pub async fn serve<P: EnabledPredicate>(
    cache: Arc<SpanCache<P>>,
    level_handle: LevelHandle,
    chance_handle: ChanceHandle,
    addr: SocketAddr,
) -> Result<(), ServeError>

Bind to addr and serve the console RPC protocol against cache.

level_handle is the LevelHandle returned by the cache’s LevelPredicate; the server uses it to apply SetCacheLevel requests and to broadcast the resulting level to every connected stream. Caller is responsible for spawning the cache’s Driver and for keeping level_handle consistent with what the cache actually uses. The future runs until the listener errors out.