Logging in `async_stream` wasn't displaying log spans correctly, this PR fixes that.
I needed to introduce a new dependency `tracing-futures` (official package from `tracing` vendor), because the core `tracing::Instrument` doesn't implement `Stream<T>`, which is required to correctly trace streaming logs.
Depends on D6246
**Question:** Should we display `user_id` in logs? Or is it sensitive data?