fix: coroutine close_async_caches was never awaited

[joshpwrk]

Problem:
When using WSGI servers with django_valkey you get the following error:
/usr/local/lib/python3.10/site-packages/django/http/response.py:335: RuntimeWarning: coroutine 'close_async_caches' was never awaited

Reason:
The current implementation connects an async connection closer to request_finished, which creates un-awaited coroutines in WSGI environments where no event loop exists. Although the implementation checks whether the Valkey object is_async, the function itself is defined as await def and thus throws an error.

Furthermore, even if users set CLOSE_CONNECTION = False, this does not prevent django from running the buggy close_async_caches function.

Solution:
Create separate sync and async handlers, and only connect the async version when async backends are detected.

[amirreza-sf80]

hello 👋
can you please provide your cache configuration, and tell me how you run your app