ClientSession teardown runs after event loop closes

Description

I often see an error in the logs about trying to close a session after the event loop is already closed:

[pulp]  | Error in atexit._run_exitfuncs:
[pulp]  | Traceback (most recent call last):
[pulp]  |   File "/src/pulpcore/pulpcore/download/factory.py", line 90, in _session_cleanup
[pulp]  |     asyncio.get_event_loop().run_until_complete(self._session.close())
[pulp]  |   File "/usr/lib64/python3.9/asyncio/base_events.py", line 622, in run_until_complete
[pulp]  |     self._check_closed()
[pulp]  |   File "/usr/lib64/python3.9/asyncio/base_events.py", line 515, in _check_closed
[pulp]  |     raise RuntimeError('Event loop is closed')
[pulp]  | RuntimeError: Event loop is closed
[pulp]  | sys:1: RuntimeWarning: coroutine 'ClientSession.close' was never awaited
[pulp]  | RuntimeWarning: Enable tracemalloc to get the object allocation traceback
[pulp]  | pulp [None]: asyncio:ERROR: Unclosed client session
[pulp]  | client_session: <aiohttp.client.ClientSession object at 0x7fcf40486eb0>

I'm not sure if that brings any immediate negative impact for the application, but I would say that is at least risky to not handle sessions lifetime correctly.

Expectation

I expect that we correctly handle the lifetime of our ClientSessions.

Reproduce

I don't have a reproducer right now.
It often happens when doing things on the content app code.

More context

What I know:

• In the context of the content app, the ClientSessions are created, shared and reused for a given Remote instance (via its download_factory 'singleton' property).
• At the logs say, currently we are trying to cleanup the session on the atexit hook, when the interpreter is existing (too late)
• "The session should be closed before the loop closing." - from aiohttp maintainer

What I dont know:

• If we can just safely ignore this forever
• How to correctly handle these sessions lifetimes

Start in pulpcore/download/factory.py at _session_cleanup around line 90, then inspect the Remote download_factory property in pulpcore/app/models/repository.py around line 581. Trace how ClientSessions are created, reused, and cleaned up relative to the event loop. Done means session cleanup occurs before loop shutdown without atexit errors, unclosed-session warnings, or unawaited-close warnings.