* Fix: Properly close aiohttp client sessions to prevent resource leaks (#12107)
- Add close() method to BaseLLMAIOHTTPHandler to properly close aiohttp ClientSession
- Create async_client_cleanup module with utility functions to close all cached async clients
- Register automatic cleanup at exit via atexit hook
- Export close_litellm_async_clients() function for manual cleanup
- Add comprehensive tests to verify resource cleanup
This fixes the "Unclosed client session" and "Unclosed connector" warnings when using acompletion with Gemini and other models that use aiohttp.
Fixes#12107
* Fix: Remove unused import to satisfy linter
* Fix: Extend cleanup to handle AsyncHTTPHandler instances used by Gemini
The original implementation only cleaned up BaseLLMAIOHTTPHandler instances,
but Gemini/Vertex AI providers use AsyncHTTPHandler objects which contain
httpx clients with aiohttp transports.
This commit extends the cleanup function to:
- Handle AsyncHTTPHandler instances by accessing their internal client
- Close both the aiohttp transport and httpx client
- Add generic fallback for any objects with aclose method
This properly fixes the resource leak warnings for all provider types.
