fix asyncio deprecation warning

[ekenyon676]

Summary

eventio_async.py relies on two asyncio APIs that are deprecated when called without a running event loop, and will emit a DeprecationWarning on any code that doesn't use the aync_read_* methods.

• asyncio.Future() — implicitly binds to the current loop via get_event_loop().
• asyncio.get_event_loop() — emits a DeprecationWarning on Python 3.10+ (and is slated for removal) when there is no running loop.

Replaced with:

• asyncio.get_running_loop().create_future() for creating futures (ReadIterator.__anext__, async_read_one, async_read).
• asyncio.get_running_loop() in _do_when_readable, caching the loop on self._loop so close() can later remove the reader from the exact loop it was registered on.

Behavior change

The old code tolerated building a read future before any loop was running. The new code must now be called from within a running loop, otherwise it will raise RuntimeError: no running event loop. Normal async for / await usage inside a coroutine is unaffected. I looked around at how this code is used in public repos (notably Home Assistant), and it appeared that nothing would break.

Testing

I wrote up a couple of example scripts (reading events via async_read_loop, async_read_one, and async_read), and confirmed the deprecation warnings no longer appear and events are read properly.