Rate-limiter latency p50/p95/p99 per category (v0.1.37 Redis RCA diagnostic)

Return a snapshot of Redis-check latency per category.

Per-category ring buffers hold the last 500 successful check latencies. Failed checks (TimeoutError → fail-open) are NOT included — they're tracked separately via the Sentry counter.

Operator use: - Verify the 100ms wait_for budget is sufficient. p99 should sit well under 100ms; if p99 creeps toward the ceiling, time for another tuning pass. - Spot a regression after a Redis/Hetzner config change.

Shape: { "auth": {"count": 423, "p50_ms": 1.2, "p95_ms": 4.8, "p99_ms": 12.3, "max_ms": 41.0}, "read": {...}, "write": {...}, "daemon": {...}, } Returns an empty dict when no checks have run yet.