[Bugfix] Fix negative local_cache_hit in P/D disaggregation metrics#34079

Prowindy wants to merge 3 commits intovllm-project:mainvllm-project/vllm:mainfrom

Prowindy:fix/negative-prompt-token-stats-pd-disaggProwindy/vllm:fix/negative-prompt-token-stats-pd-disaggCopy head branch name to clipboard