add log for pd nixl

[hiworldwzj]

No description provided.

[gemini-code-assist]

Code Review

This pull request introduces GPU timing measurements for memory page copy operations and logs the elapsed time. It also adds latency tracking for adding remote agents in the NIXL KV transporter. The feedback suggests defensively checking that both copy_start_event and copy_end_event are not None before calculating the elapsed time to prevent potential AttributeError exceptions.

[gemini-code-assist]

To ensure robust defensive programming, verify that both copy_end_event and copy_start_event are not None before calling elapsed_time to prevent potential AttributeError exceptions.

Suggested change

	if copy_end_event is not None:
	copy_end_event.synchronize()
	read_page_gpu_time_ms = copy_start_event.elapsed_time(copy_end_event)
	if copy_end_event is not None and copy_start_event is not None:
	copy_end_event.synchronize()
	read_page_gpu_time_ms = copy_start_event.elapsed_time(copy_end_event)