Better support for Dragonfly memcache facade

[emyfops]

I've bumped into issues when attempting to use gets and gats with a memcache compatible facade for DragonFly

They did not fully implement the basic text protocol have in some cases changed the behavior of some commands
After further researching, I've found that the get and gat commands can return more than just one key and decided to add a simple condition in Gets and GetsAndTouch to specify whether the user wants to use CAS commands

I've made sure that this change would not break existing codebases but more testing would be great

https://docs.memcached.org/protocols/basic/#get

[yeqown]

could you provides tcp packets to help me analyzing?

In this PR the API signature changed which breaks, and I wonder how the Dragonfly implying the protocol? If they have a different spec, maybe we should make new API for this.

[emyfops]

For the moment, dragonfly does not support CAS commands including gets and gats
This is an error on their behalf and will change their documentation accordingly
We don't know when these commands will be supported

Maybe it's not a good idea to add a single argument for this edge case, tell me what you think

[yeqown]

Yes, we'd better not change the present API

[emyfops]

@yeqown this issue should've been fixed in this dragonflydb/dragonfly#5087