[queues] correct DurableObject to DurableObjectNamespace & remove…

… constructor block (#14529)

* correct `DurableObject` to `DurableObjectNamespace`

* remove constructor block and made `env` public

* add failure response

* Update content/queues/examples/use-queues-with-durable-objects.md

Co-authored-by: Maddy <130055405+Maddy-Cloudflare@users.noreply.github.com>

---------

Co-authored-by: Maddy <130055405+Maddy-Cloudflare@users.noreply.github.com>

content/queues/examples/use-queues-with-durable-objects.md

@@ -48,7 +48,7 @@ filename: src/index.ts
 ---
 interface Env {
   YOUR_QUEUE: Queue;
-  YOUR_DO_CLASS: DurableObject;
+  YOUR_DO_CLASS: DurableObjectNamespace;
 }
 
 export default {
@@ -74,17 +74,12 @@ export default {
       // This would return "wrote to queue", but you could return any response.
       return response;
     }
+		return new Response("userId must be provided", { status: 400 });
   }
 }
 
 export class YourDurableObject implements DurableObject {
-  constructor(public state: DurableObjectState, env: Env) {
-      this.state = state;
-      // Ensure you pass your bindings and environment variables into
-      // each Durable Object when it is initialized
-      this.env = env;
-    }
-  }
+  constructor(private state: DurableObjectState, private env: Env) {}
 
   async fetch(request: Request) {
     // Error handling elided for brevity.