feat: add support for BLMPOP command

[EricHayter]

Adding support for the BLMPOP redis command. The command description can be found here.

Resolves #3876

[EricHayter]

I'm working on implementing the test cases but I ran into a problem when providing non-integer or a 0 to the timeout argument. It seems like the timeout argument is being parsed as a the numkeys argument.

127.0.0.1:6379> BLMPOP 0 1 empty empty LEFT COUNT 10
(error) ERR at least 1 input key is needed for this command
127.0.0.1:6379> BLMPOP 0.01 1 empty empty LEFT COUNT 10
(error) ERR value is not an integer or out of range

It could be an issue with how the command is being registered but it's not clear what values should be used instead of the following?:

<< CI{"BLMPOP", CO::WRITE | CO::SLOW | CO::VARIADIC_KEYS, -5, 3, 3, acl::kBLMPop}.HFUNC(
             BLMPop)

I did check the redis arguments (as suggested in command_id.h) but it's not clear what I would use as the last key index?

[romange]

yeah, sorry for this. you probably need to hack DetermineKeys function in transaction.cc.
I am guessing num_keys_index is deduced incorrectly. The command structure in redis is not uniform and we wrote a single, not very elegant function that handles "exceptions".

[romange]

looks good! a few minor comments

[romange]

Thank you @EricHayter

[romange]

@EricHayter there is one thing that is missing - CO::NO_AUTOJOURNAL. Basically for such commands we need to send a different command for replication, so we disable the default journaling. Also OpPop should be called with journal_rewrite=true