DiagnosticPublisher attempts to use the main asyncio event loop from worker threads (which fails)

[pavel-kirienko]

Here, the call to ensure_future is invalid because emit can be invoked from any thread while we must use the asyncio loop from the node thread:

pycyphal/pycyphal/application/diagnostic.py

Line 187 in 40e1482

self._fut = asyncio.ensure_future(self._publish(dcs_rec))

Related: #334