Collection Speed Improvements (#874)

* Add UltraSlimCollectionSerializer and update CollectionViewSet for optimized listing

- Introduced UltraSlimCollectionSerializer for efficient data representation.
- Updated CollectionViewSet to use the new serializer for list actions.
- Enhanced queryset optimizations with prefetching for related images.
- Modified frontend components to support SlimCollection type for better performance.

* Optimize rendering of collection cards by adding a unique key to the each block

backend/server/adventures/serializers.py

@@ -655,4 +655,49 @@ class CollectionInviteSerializer(serializers.ModelSerializer):
     class Meta:
         model = CollectionInvite
         fields = ['id', 'collection', 'created_at', 'name', 'collection_owner_username', 'collection_user_first_name', 'collection_user_last_name']
-        read_only_fields = ['id', 'created_at']
+        read_only_fields = ['id', 'created_at']
+
+class UltraSlimCollectionSerializer(serializers.ModelSerializer):
+    location_images = serializers.SerializerMethodField()
+    location_count = serializers.SerializerMethodField()
+    
+    class Meta:
+        model = Collection
+        fields = [
+            'id', 'user', 'name', 'description', 'is_public', 'start_date', 'end_date', 
+            'is_archived', 'link', 'created_at', 'updated_at', 'location_images', 
+            'location_count', 'shared_with'
+        ]
+        read_only_fields = fields  # All fields are read-only for listing
+
+    def get_location_images(self, obj):
+        """Get primary images from locations in this collection, optimized with select_related"""
+        # Filter first, then slice (removed slicing)
+        images = ContentImage.objects.filter(
+            location__collections=obj
+        ).select_related('user').prefetch_related('location')
+
+        return ContentImageSerializer(
+            images,
+            many=True,
+            context={'request': self.context.get('request')}
+        ).data
+
+    def get_location_count(self, obj):
+        """Get count of locations in this collection"""
+        # This uses the cached count if available, or does a simple count query
+        return obj.locations.count()
+
+    def to_representation(self, instance):
+        representation = super().to_representation(instance)
+
+        # make it show the uuid instead of the pk for the user
+        representation['user'] = str(instance.user.uuid)
+        
+        # Make it display the user uuid for the shared users instead of the PK
+        shared_uuids = []
+        for user in instance.shared_with.all():
+            shared_uuids.append(str(user.uuid))
+        representation['shared_with'] = shared_uuids
+        return representation
+