Expose collections field in ActivityData model

[osvaldobtorres]

The REST API for Activity Feeds V3 returns collections for activities when collection refs are present in the activity:

{
    "activities": [
        {
            "id": "...",
            "text": "...",
            "collections": { ... }
        }
    ]
}

The autogenerated API layer already maps the collections field correctly:

// packages/stream_feeds/lib/src/generated/api/model/activity_response.g.dart

ActivityResponse _$ActivityResponseFromJson(Map<String, dynamic> json) =>
    ActivityResponse(
      collections: (json['collections'] as Map<String, dynamic>).map(
        (k, e) => MapEntry(
            k, EnrichedCollectionResponse.fromJson(e as Map<String, dynamic>)),
      ),
      ...
    )

However, in the SDK the ActivityData model defined in packages/stream_feeds/lib/src/models/activity_data.dart does not include a property for collections, the data is also not propagated when mapping ActivityResponse to ActivityData, as shown below:

extension ActivityResponseMapper on ActivityResponse {
  /// Converts this API activity response to a domain [ActivityData] instance.
  ///
  /// This is a simplified implementation that works with the current project state.
  /// Some fields are simplified or use placeholders until all dependencies are implemented.
  ActivityData toModel() {
    return ActivityData(
      attachments: attachments,
      bookmarkCount: bookmarkCount,
      commentCount: commentCount,
      comments: [...comments.map((c) => c.toModel())],
      createdAt: createdAt,
      currentFeed: currentFeed?.toModel(),
      deletedAt: deletedAt,
      editedAt: editedAt,
      expiresAt: expiresAt,
      feeds: feeds,
      filterTags: filterTags,
      id: id,
      interestTags: interestTags,
      isWatched: isWatched,
      latestReactions: [...latestReactions.map((r) => r.toModel())],
      location: location?.let(
        (it) => LocationCoordinate(
          latitude: it.lat,
          longitude: it.lng,
        ),
      ),
      mentionedUsers: [...mentionedUsers.map((u) => u.toModel())],
      moderation: moderation?.toModel(),
      notificationContext: notificationContext,
      ownBookmarks: [...ownBookmarks.map((b) => b.toModel())],
      ownReactions: [...ownReactions.map((r) => r.toModel())],
      parent: parent?.toModel(),
      poll: poll?.toModel(),
      popularity: popularity,
      hidden: hidden,
      preview: preview,
      reactionCount: reactionCount,
      reactionGroups: {
        for (final entry in reactionGroups.entries)
          entry.key: entry.value.toModel(),
      },
      score: score,
      searchData: searchData,
      shareCount: shareCount,
      text: text,
      type: type,
      updatedAt: updatedAt,
      user: user.toModel(),
      visibility: visibility.toModel(),
      visibilityTag: visibilityTag,
      custom: custom,
    );
  }
}

As a result, collection data is not accessible in Flutter clients even though it is returned by the API.

The documentation suggests collections are returned: https://getstream.io/activity-feeds/docs/flutter/collections/

Please consider adding a collections field to ActivityData and mapping it from ActivityResponse so this data can be accessed in the Flutter SDK.

Thank you!