Ability to call keys in specific key slot

[creker]

Right now keys command is not specifying any key slot and executed on an arbitrary node. It would be useful if rueidis would allow locking keys to specific key slot.

My use-case is that I want to list all keys that are guaranteed to land in the same key slot. For example, given the following keys

foo{a}:1
foo{b}:2
foo{b}:3
foo{c}:4
foo{d}:5

I want to execute keys foo{b}:* and expect it to return foo{b}:2 and foo{b}:3. In order to do that now I have to send that command to all nodes. That seems wasteful.

One way this could be implemented is to add new method to internal/cmds/Keys or internal/cmds/KeysPattern that would tell rueidis to use the given pattern in key slot calculation. For example, for Keys it could be something like PatternKeySlot that would do the same thing as Pattern but would also calculate key slot. For KeysPattern it could be KeySlot that would use previously specified pattern to calculate key slot.

[Rueian]

This is a good idea and there might be other commands that need this as well.

So, I think we can add a SetSlot(...) function to the Completed struct. For example:

cmd := client.B().Keys().Pattern("foo{a}:1").Build().SetSlot("a")