Reports whether a binding is Queues-producer-shaped.

Read by BindingRegistry.queue, which cast its binding unvalidated until this existed — the same hole M52c closed on D1 and M52d on Durable Objects, and the last one left in this family. A missing queues.producers stanza or a name typo let the application boot clean, report up from the cloudflare health indicator, and fail on the first add() or publish() with a bare TypeError pointing at nothing.