Shared builder for RedisMulti and RedisPipeline.
It queues commands. Use call for any command that has no method here.
Results are raw replies (for example HGETALL gives a flat list).
Result of SCAN, HSCAN, SSCAN and ZSCAN.
cursor is '0' when the scan is done.
items is a flat list (field, value, ... for HSCAN and member, score, ... for ZSCAN).