Explicitly don't support 'model3d' cards

Fixes #597

src/experimental/parser/unifiedcard.nim

@@ -66,6 +66,8 @@ proc parseMedia(component: Component; card: UnifiedCard; result: var Card) =
       durationMs: videoInfo.durationMillis,
       variants: videoInfo.variants
     )
+  of model3d:
+    result.title = "Unsupported 3D model ad"
 
 proc parseUnifiedCard*(json: string): Card =
   let card = json.fromJson(UnifiedCard)

src/experimental/types/unifiedcard.nim

@@ -48,7 +48,7 @@ type
     vanity*: string
 
   MediaType* = enum
-    photo, video
+    photo, video, model3d
 
   MediaEntity* = object
     kind*: MediaType
@@ -102,4 +102,5 @@ proc enumHook*(s: string; v: var MediaType) =
   v = case s
       of "video": video
       of "photo": photo
+      of "model3d": model3d
       else: echo "ERROR: Unknown enum value (MediaType): ", s; photo