Function refresh_rate_limiter_gauges 

pub fn refresh_rate_limiter_gauges(
    engine: &RateLimitEngine,
    obs: &Observability,
)

Refresh the rate-limiter observation gauges from the CURRENT engine at scrape time (#132) — the same snapshot model as refresh_observation_gauges: the walk lives on the dataplane (the extensions-side engine must stay free of observability imports), the hot check path stays pure atomics with zero metrics coupling, and the observability side only records what it is handed. Both gauges are aggregate and unlabeled — cardinality is never per key. The eviction figure resets when a reload rebuilds the engine (documented family caveat).