DEV: Replace computed macros with getters in PostStream (#36758)

Refactor `PostStream` by replacing Ember's computed macros (`@or`,
`@and`, `@not`, `@equal`) with native getters and `@dependentKeyCompat`.
This modernizes the codebase to align with current Ember conventions and
improves readability and maintainability. No functional changes
introduced.

frontend/discourse/app/models/post-stream.js

@@ -1,7 +1,6 @@
 import { cached, tracked } from "@glimmer/tracking";
 import { get } from "@ember/object";
 import { dependentKeyCompat } from "@ember/object/compat";
-import { and, equal, not, or } from "@ember/object/computed";
 import { schedule } from "@ember/runloop";
 import { service } from "@ember/service";
 import { isEmpty } from "@ember/utils";
@@ -73,16 +72,48 @@ export default class PostStream extends RestModel {
   @trackedArray stream = [];
   @trackedArray userFilters = [];
 
-  @or("loadingAbove", "loadingBelow", "loadingFilter", "stagingPost") loading;
-  @not("loading") notLoading;
-  @equal("filter", "summary") summary;
-  @and("notLoading", "hasPosts", "lastPostNotLoaded") canAppendMore;
-  @and("notLoading", "hasPosts", "firstPostNotLoaded") canPrependMore;
-  @not("firstPostPresent") firstPostNotLoaded;
-  @not("loadedAllPosts") lastPostNotLoaded;
-
   _identityMap = {};
 
+  @dependentKeyCompat
+  get loading() {
+    return (
+      this.loadingAbove ||
+      this.loadingBelow ||
+      this.loadingFilter ||
+      this.stagingPost
+    );
+  }
+
+  @dependentKeyCompat
+  get notLoading() {
+    return !this.loading;
+  }
+
+  @dependentKeyCompat
+  get firstPostNotLoaded() {
+    return !this.firstPostPresent;
+  }
+
+  @dependentKeyCompat
+  get lastPostNotLoaded() {
+    return !this.loadedAllPosts;
+  }
+
+  @dependentKeyCompat
+  get canAppendMore() {
+    return this.notLoading && this.hasPosts && this.lastPostNotLoaded;
+  }
+
+  @dependentKeyCompat
+  get canPrependMore() {
+    return this.notLoading && this.hasPosts && this.firstPostNotLoaded;
+  }
+
+  @dependentKeyCompat
+  get summary() {
+    return this.filter === "summary";
+  }
+
   @cached
   @dependentKeyCompat
   get postsWithPlaceholders() {