Atomic rate-limit snapshots

RedisRateLimiterStore implements the optional RateLimiterSnapshotStoreInterface. A snapshot reads the count and remaining lifetime together and can record an attempt in the same Lua operation.

$snapshot = $store->snapshot('catalog', interval: 60);
$readOnly = $store->snapshot('catalog', interval: 60, increment: false);

The result has integer operations and ttl fields. The interval must be positive and uses seconds. The first increment starts expiry; later increments do not extend it. Remaining milliseconds round up to seconds so a live key does not appear expired. A missing or permanent key reports zero remaining TTL.

RateLimiter prefers this capability when supplied and retains its existing fallback for custom stores implementing only RateLimiterStoreInterface. Native Redis snapshots require one evaluation rather than separate count and TTL reads.