Rename `ir.clusters.visitors.Queue`

[enwask]

The Queue cluster visitor is confusingly named for something that performs a divide-and-conquer process; I'd propose renaming it to something but not sure what. Specifically making this issue because I'm starting to write some threaded code relating to these Queues and will be making heavy use of the built-in queue.Queue which clashes.

Didn't want to go ahead and rename this yet as there are a bunch of uses in subclassed visitors (not sure if these are extended in pro) so I think it's a reasonably nontrivial change

[JDBetteridge]

Ooof, clashing with a Python built-in is not ideal! Is this exposed and/or used in the public API or just internally?

[EdCaunt]

Purely used internally iirc