key_expr method for PullSubscriber and Queryable

[milyin]

obejcts Publisher and Subscriber have public key_expr method: https://github.com/eclipse-zenoh/zenoh/blob/8df2d0d3dde2fc911a357d214344a8a9e0d72c93/zenoh/src/publication.rs#L227-L230 https://github.com/eclipse-zenoh/zenoh/blob/8df2d0d3dde2fc911a357d214344a8a9e0d72c93/zenoh/src/subscriber.rs#L747-L749

But there is no such method for PullSubscriber and Queryable. I think they have to be added for API consistency

[Mallets]

PullSubscriber has been removed in https://github.com/eclipse-zenoh/zenoh/tree/dev/1.0.0. Therefore, the issue only applies to Queryable.