Improve shared channel error handling

[lquerel]

In rust/otap-dataflow/crates/engine/src/shared/message.rs (line 292)

It seems we are mapping all errors to RecvError::Closed. Better to check for TryRecvError::Empty and TryRecvError::Disconnected (for both tokio::x::mpsc and flume) and handle accordingly.

See: #1697 (comment)