Remove event_loop fixture

[seifertm]

This PR removes the deprecated event_loop fixture along with the associated warnings, such as the unclosed loop warning, the warning about requesting event_loop in async fixtures and tests, and the warning about multiple loops being requested in the same test.

This patch follows up the deprecation of the event_loop fixture in v0.22/v0.23 and represents a major cleanup of the pytest-asyncio code base.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.60%. Comparing base (22b4080) to head (44162c4).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1106      +/-   ##
==========================================
- Coverage   90.84%   90.60%   -0.25%     
==========================================
  Files           2        2              
  Lines         579      500      -79     
  Branches       77       64      -13     
==========================================
- Hits          526      453      -73     
+ Misses         32       30       -2     
+ Partials       21       17       -4     

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[Dreamsorcerer]

I'm not clear how event_loop should be replaced in sync test functions? I had previously assumed from the warnings, that event_loop was only deprecated for async functions.

[Dreamsorcerer]

Hmm, we've got some rather awkward tests going on...

We have things like:

def test_one_thousand_round_trip_websocket_text_messages(
    event_loop: asyncio.AbstractEventLoop,
    aiohttp_client: AiohttpClient,
    benchmark: BenchmarkFixture,
) -> None:
    ...

    @benchmark
    def _run() -> None:
        event_loop.run_until_complete(run_websocket_benchmark())

But, aiohttp_client fixture is async, so it must be running in a loop context. So, if I create a new loop or something in this test, then I get problems like:

RuntimeError: Task <Task pending name='Task-34' coro=<RequestHandler.shutdown() running at /Users/runner/work/aiohttp/aiohttp/aiohttp/web_protocol.py:336> cb=[gather.<locals>._done_callback() at /Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/asyncio/tasks.py:764]> got Future <Future pending> attached to a different loop

[Dreamsorcerer]

OK, seem to have resolved it with:

@pytest.fixture
async def event_loop() -> asyncio.AbstractEventLoop:
    return asyncio.get_running_loop()