NewRedisMap uses the global redisClient with no prefix (API-compat).

NewRedisMapClient uses a *custom* client with no prefix.

NewRedisMapClientWithPrefix uses a custom client and a prefix for keys.

SetRedisClientForUtils sets the global Redis client.

RedisSafeMap is a Redis-backed map with an optional prefix, plus a companion Redis Set that tracks our keys to allow fast Len/Keys/Range.