Unable to run concurrent asyncio processes about mmpy_bot

[unode]

This needs further looking into but we have two execution paths.

Regular (non-async) functions are handled by a thread pool, currently hardcoded to handle up to 10 concurrent requests.
Requests run outside the MainThread and don't block its execution.

async functions are currently handled by the MainThread. They are expected to await as soon as possible to release the work to other tasks.
This means that in the above code, where time.sleep(5) is used, await asyncio.sleep(5) should have been used instead.

However this is rather unintuitive as it blocks new requests.
The source of the issue is here.

This needs further reflection as I'm not sure threading the work is safe. @jneeven 's advice would be welcome here as this looks like a deliberate design choice.