avoid deprecated get_event_loop...
avoid deprecated get_event_loop
use our own `async_helpers.get_asyncio_loop` to track the global event loop
script magics use dedicated background asyncio loop
instead of trying to work on the main loop, which may or may not exist
_AsyncIOProxy wraps background script objects to transfer awaitables across loops
only works for coroutine methods, which might be good enough? Works for read, etc.
