[BugFix] Ensure appropriate guards in destructors

[njhill]

Care must be taken in destructors to check for attributes that might not exist if the constructor failed.

Some secondary startup error logs have been seen recently due to this.

[njhill]

Executors always have an explicit owner that calls shutdown() so don't need a destructor.

[gemini-code-assist]

Code Review

This pull request aims to make destructors safer by adding guards to prevent AttributeError when an object's __init__ method fails before all attributes are initialized. The changes across several files use getattr to safely access attributes in __del__ or shutdown methods, which is a good practice.

However, I've identified a potential regression in vllm/distributed/device_communicators/quick_all_reduce.py. The change from getattr to hasattr alters the logic for re-entrant calls to the close() method, which could lead to a crash if a cleanup function is called with a null pointer. I've suggested reverting this specific change to maintain the original, safer behavior. The other changes look correct and improve the robustness of the code.