Light Client: subxt API will do nothing after smoldot thread panic.

Here is the example:

let mut sub = edge
                .api()
                .await
                .blocks()
                .subscribe_finalized()
                .await
                .unwrap();
while let Ok(block) = sub.next().await.unwrap() {
}

After several blocks had been subscribed, smoldot thread reported an error:

thread 'smoldot-light-2' panicked at /home/gitlab-workspaces/.cargo/registry/src/index.crates.io-6f17d22bba15001f/smoldot-light-0.14.0/src/runtime_service.rs:472:34: called `Result::unwrap()` on an `Err` value: ()

But let Ok(block) = sub.next().await.unwrap() will keep blocking there without panic, so there is no way to handle this kind of underlying error and causing the program stuck forever.

Start with the light-client subscription example in the issue and trace how the smoldot thread failure reaches sub.next(). Determine where the underlying error is lost and how the subscription signals termination. Done means a smoldot failure no longer leaves the subscription blocked forever and can be handled by the caller.