[fix] Convert TransferQueueController to non-detached Ray actor to prevent resource leaks

[0oshowero0]

Background

Previously, interface.py created a detached Ray actor for the TransferQueueController. Although a tq.close() method was provided to terminate the actor, it might not be executed in the event of an unexpected crash or error. This could cause the detached actor to persist indefinitely, leading to resource leaks.

Changes

1. Lifecycle Management: Converted TransferQueueController from a detached actor to a standard (non-detached) actor. Its lifecycle is now tied to the driver process.
2. Instance Handling: Utilized a global variable to store and manage the actor handle.
3. Cleanup Logic: Improved the robustness of the tq.close() method.

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Pull request overview

This PR changes how TransferQueueController is created and tracked so it is no longer a detached Ray actor, reducing the risk of orphaned controllers when tq.close() is not executed.

Changes:

• Introduces a module-level _TRANSFER_QUEUE_CONTROLLER handle to store the controller actor reference.
• Creates TransferQueueController as a normal (non-detached) named actor and reuses the cached handle where possible.
• Updates close() to attempt to kill the controller via the cached handle.

Comments suppressed due to low confidence (1)

transfer_queue/interface.py:252

• close() now attempts to kill the controller twice: first via the cached handle and then again by fetching the named actor. This is redundant work and makes the shutdown logic harder to reason about (and can produce avoidable errors/logs). Consider a single best-effort kill path (e.g., kill cached handle if present else try ray.get_actor()).

    if _TRANSFER_QUEUE_CONTROLLER:
        ray.kill(_TRANSFER_QUEUE_CONTROLLER)
        _TRANSFER_QUEUE_CONTROLLER = None

    try:
        controller = ray.get_actor("TransferQueueController")
        ray.kill(controller)
    except Exception:

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CLA Signature Pass

0oshowero0, thanks for your pull request. All authors of the commits have signed the CLA. 👍