[BugFix] Fix --disable-log-stats in V1 server mode

[njhill]

Also sum gpu blocks across DP ranks when reporting the num_gpu_blocks metric.

Both introduced by #15755

There is a test for this but it's not running on V1 yet. Will look at changing that: https://github.com/vllm-project/vllm/blob/main/tests/metrics/test_metrics.py

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[njhill]

I think the test failure is also happening on main. I will look into that too