asyncpg __del__ methods call asyncio APIs directly, which isn't guaranteed to work and indeed, doesn't work

Nadie ha tomado este issue todavía.

asyncpg has several `__del__` methods that call into asyncio APIs. But... you can't safely call into asyncio APIs from a `__del__` method, because `__del__` methods can be run in arbitrary threads, or at arbitrary moments when the loop's internal data structures are in an inconsistent state.

Discovered here: https://github.com/python-trio/trio-asyncio/issues/44

Looking at the traceback in that issue, I suspect that the reason this hasn't been noticed before is that the `__del__` method ultimately ends up calling `loop.call_soon(...)`. And if you do that from another thread, then with regular asyncio, things will mostly seem to work – it won't actually wake up the loop the way `call_soon_threadsafe` would, but if the loop is still running then it will eventually get run, and the default `call_soon` will not explode or otherwise notice if it's called from the wrong thread. But in that issue, someone's using asyncpg with an alternative asyncio loop that fails when `call_soon` is called from the wrong thread, and this breaks asyncpg.

I guess asyncpg should go through all its `__del__` methods and wrap them in a `loop.call_soon_threadsafe`?

Empieza por inventariar los métodos __del__ de asyncpg y las rutas de loop.call_soon implicadas por el issue enlazado de Trio. Comprueba cada ruta de limpieza frente a las preocupaciones sobre la seguridad de los hilos y el estado del loop descritas allí. Se considerará terminado cuando el comportamiento de limpieza afectado funcione con implementaciones alternativas del loop de asyncio sin llamadas directas inseguras.

Escrito por el modelo de indexación a partir del texto del issue.