switched from crossbeam to flume, for async support + fixed Instance::report_err() and Instance::new_connection_join_namespace()

src/core/instance/updater.rs

@@ -1,4 +1,4 @@
-use crossbeam::channel::Receiver;
+use flume::Receiver;
 use tracing::{error, trace, warn};
 use std::borrow::BorrowMut;
 use std::sync::Arc;