[Bugfix] Fix eviction cached blocked logic

[simon-mo]

There was a logic error in #21281 causing crashes that triggered by retaining blocks where hashes are already reset.

Tested manually. Crashes before when running large set of benchmarks, no more crashes afterward.

[gemini-code-assist]

Code Review

This pull request fixes a critical logic error in the KV cache eviction mechanism. It also enhances the benchmarking scripts, including the ability to clamp the maximum output length and display request statistics. I've identified potential issues in the new benchmarking code related to input validation and handling edge cases and have provided suggestions to address them.

[github-actions]

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[njhill]

Thanks @simon-mo. Was my typo in a review suggestion ... should have been not blocks_by_id of course 😅