Support HEXPIRE

[brkn]

Redis, since v7.4.0, enables a field inside a hash key to be expired

https://redis.io/docs/latest/commands/hexpire/

I am not sure how would API look like

hash = Kredis.hash "myhash"
hash.update("key" => "value", "key2" => "value2") # => HSET myhash "key", "value", "key2", "value2"
hash.expire_keys("key2", "key", in: 2.minutes) # => HEXPIRE myhash 120 FIELDS 2 "key2" "key"