[SameRainbows]

Fixes #463

Description

When routes configure a groupId, the group identifier is appended to the rate-limit key, but each route previously received a distinct storage partition:

• In LocalStore.prototype.child, a new LocalStore instance was created with a fresh LRU cache per route, meaning counters on identical keys across different routes never collided.
• In RedisStore.prototype.child, the namespace was hardcoded to routeOptions.routeInfo.method + routeOptions.routeInfo.url, prefixing the route before the key.

As a result, N routes in the same group each allowed the full max quota, rather than sharing a single quota as intended.

Changes

• In LocalStore.prototype.child: when routeOptions.groupId is provided, reuse the parent store's LRU cache so matching group keys collide as expected.
• In RedisStore.prototype.child: when routeOptions.groupId is provided, use the group identifier as the key prefix namespace instead of method + URL.
• Both stores preserve the existing per-route behavior when no groupId is present.
• Added regression tests in test/group-rate-limit.test.js verifying shared group counters, independent counters without groupId, and RedisStore child namespacing.
• Added Redis integration coverage in test/redis-rate-limit.test.js verifying shared counters when Redis is running.