Sub task of #617
Background
There is no consolidated documentation for the library's observability surface.
Scope
Write a metric catalog (every kvcache_* metric, its type, labels, and meaning), a tracing setup guide (exporter config, span hierarchy), and scrape-config guidance. Cover the EPP-embedded case explicitly: kvcache_* metrics share EPP's controller-runtime Registry and appear at EPP's /metrics unchanged, so no separate scrape endpoint exists in the library.
EPP-side scrape configuration links out to the llm-d-router observability docs.
Sub task of #617
Background
There is no consolidated documentation for the library's observability surface.
Scope
Write a metric catalog (every kvcache_* metric, its type, labels, and meaning), a tracing setup guide (exporter config, span hierarchy), and scrape-config guidance. Cover the EPP-embedded case explicitly: kvcache_* metrics share EPP's controller-runtime Registry and appear at EPP's
/metricsunchanged, so no separate scrape endpoint exists in the library.EPP-side scrape configuration links out to the llm-d-router observability docs.