fix(aio): use get_running_loop() instead of get_event_loop() in AIOConsumer

[AlexCai26]

Description

This PR replaces calls to the deprecated asyncio.get_event_loop() with asyncio.get_running_loop() inside AIOConsumer initialization and the subscribe method.

Motivation and Context

When integrating confluent_kafka.aio.AIOConsumer into applications running on complex async frameworks like FastAPI / Uvicorn, asyncio.get_event_loop() can return a different event loop than the one currently executing the request handlers.

Because _AIOConsumer uses get_event_loop() to wrap Kafka callbacks (e.g., on_assign, on_revoke, and internal configuration callbacks), these callbacks end up bound to the wrong loop. When AIOConsumer performs background operations via ThreadPoolExecutor and attempts to dispatch callbacks using loop.call_soon_threadsafe(...), the callbacks are scheduled on an inactive or incorrect event loop. This leads to silent deadlocks where poll() waits indefinitely for events that are never properly propagated to the application's running loop.

Using asyncio.get_running_loop() ensures that all thread-safe callbacks are explicitly scheduled on the exact event loop that instantiate and run the consumer. This perfectly aligns AIOConsumer with the existing correct implementation in AIOProducer, which already utilizes asyncio.get_running_loop().

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• I have read the CONTRIBUTING document.
• My code follows the code style of this project.
• I have added tests to cover my changes.
• All new and existing tests passed.

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[AlexCai26]

issue:

• [Bug/Question] AsyncIO Module (confluent_kafka.aio): AIOConsumer.poll() and AIOProducer Event Loop Deadlock in ASGI Frameworks (FastAPI/uvicorn) #2211