fix: restore UserNewsResource flat-properties structure to preserve equals() semantics

Storing newsResource+userData directly as data class fields caused equals()
to compare userData.shouldHideOnboarding, breaking ForYouViewModelTest.
Restored the original internal primary constructor with flat computed fields,
adding bookmarkNote as an additional flat property.

Co-Authored-By: Claude <noreply@anthropic.com>

core/model/src/main/kotlin/com/google/samples/apps/nowinandroid/core/model/data/UserNewsResource.kt

@@ -22,28 +22,37 @@ import kotlinx.datetime.Instant
  * A [NewsResource] with additional user information such as whether the user is following the
  * news resource's topics and whether they have saved (bookmarked) this news resource.
  */
-data class UserNewsResource(
-    val newsResource: NewsResource,
-    val userData: UserData,
+data class UserNewsResource internal constructor(
+    val id: String,
+    val title: String,
+    val content: String,
+    val url: String,
+    val headerImageUrl: String?,
+    val publishDate: Instant,
+    val type: String,
+    val followableTopics: List<FollowableTopic>,
+    val isSaved: Boolean,
+    val hasBeenViewed: Boolean,
+    val bookmarkNote: String?,
 ) {
-    val id: String get() = newsResource.id
-    val title: String get() = newsResource.title
-    val content: String get() = newsResource.content
-    val url: String get() = newsResource.url
-    val headerImageUrl: String? get() = newsResource.headerImageUrl
-    val publishDate: Instant get() = newsResource.publishDate
-    val type: String get() = newsResource.type
-    val followableTopics: List<FollowableTopic>
-        get() = newsResource.topics.map { topic ->
+    constructor(newsResource: NewsResource, userData: UserData) : this(
+        id = newsResource.id,
+        title = newsResource.title,
+        content = newsResource.content,
+        url = newsResource.url,
+        headerImageUrl = newsResource.headerImageUrl,
+        publishDate = newsResource.publishDate,
+        type = newsResource.type,
+        followableTopics = newsResource.topics.map { topic ->
             FollowableTopic(
                 topic = topic,
                 isFollowed = topic.id in userData.followedTopics,
             )
-        }
-    val isSaved: Boolean get() = newsResource.id in userData.bookmarkedNewsResources
-    val hasBeenViewed: Boolean get() = newsResource.id in userData.viewedNewsResources
-    val bookmarkNote: String?
-        get() = userData.bookmarkNotes[newsResource.id].takeIf { !it.isNullOrBlank() }
+        },
+        isSaved = newsResource.id in userData.bookmarkedNewsResources,
+        hasBeenViewed = newsResource.id in userData.viewedNewsResources,
+        bookmarkNote = userData.bookmarkNotes[newsResource.id].takeIf { !it.isNullOrBlank() },
+    )
 }
 
 fun List<NewsResource>.mapToUserNewsResources(userData: UserData): List<UserNewsResource> =