[Bugfix] fix the incorrect use of numpy's sum on tensors.

[wangx700]

What this PR does / why we need it?

Fix the incorrect use of numpy's sum function on PyTorch tensors.

Does this PR introduce any user-facing change?

How was this patch tested?

• vLLM version: 86e178f7c4d8c3b0eaf3c8e3f810a83f63b90e24
• vLLM main: vllm-project/vllm@86e178f

[gemini-code-assist]

Code Review

This pull request correctly fixes an issue where Python's built-in sum() was used on a PyTorch tensor, replacing it with torch.sum().item(). However, the refactoring also introduces a critical bug by removing the definition of the max_num_scheduled_tokens variable, which is used later in the function. This will lead to a NameError at runtime. I've added a comment to address this.

[github-actions]

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