FIX: Cache breadcrumb-item template (#27585)

…to avoid re-evaulation right before destroying.

With `DeferredTrackedSet` we delay both adding and removing elements from the set. That means when you're transitioning between routes, and breadcrumbs change, both old and new breadcrumbs are rendered (briefly, in a first render pass)

And since the arguments for the old breadcrumbs can be (and often are) destroyed - it would blow up the renderer. By caching the template it will reuse it in that first pass.

---

No test because I couldn't figure out a synthetic test setup where you have breadcrumbs in a deeply nested route and where you navigate from that route to one of the parent routes.

app/assets/javascripts/discourse/app/components/d-breadcrumbs-item.gjs

@@ -1,4 +1,5 @@
 import Component from "@glimmer/component";
+import { cached } from "@glimmer/tracking";
 import { service } from "@ember/service";
 
 export default class DBreadcrumbsItem extends Component {
@@ -23,6 +24,7 @@ export default class DBreadcrumbsItem extends Component {
     }
   }
 
+  @cached
   get templateForContainer() {
     // Those are evaluated in a different context than the `@linkClass`
     const { label } = this.args;