Adding `next` and `send_output` requires an async threadpool as the
communication Layer defined by the Middleware Layer returns an async Future
stream.
I solve this issue by adding a tokio runtime on a separater thread that is connected with two channels.
One for sending data and one for receiving data.
Those channel are then exposed synchronously to Python. This should not be cause for
concern as channel are really fast.
Looking at Zenoh Python client, they are heavily using `pyo3-asyncio` implementation
of futures to pass Rust futures into Python.
This can be a solution as well, but, from previous experiment, I'm concerned about performance on such
solution. I have experienced that putting futures from Rust into the `asyncio` queue to be slow.
I'm concerned also by mixing `async` and `sync` code in Python, as it might be blocking. This might requires 2 threadpool in Python.
This might seem as heavy overhead for some operations.
haixuanTao