Fixed RankDescriptions not using custom serializer.

core/src/commonMain/kotlin/cn/rdlevel/rdkt/core/settings/Ranking.kt

@@ -83,7 +83,7 @@ public data class RankMaxMistakes(
     }
 
     public object Serializer : KSerializer<RankMaxMistakes> {
-        private val listSerializer = ListSerializer(Int.Companion.serializer())
+        private val listSerializer = ListSerializer(Int.serializer())
 
         override val descriptor: SerialDescriptor = listSerializer.descriptor
 
@@ -113,7 +113,7 @@ public data class RankMaxMistakes(
 /**
  * Represents the description for each rank in a level.
  */
-@Serializable
+@Serializable(RankDescriptions.Serializer::class)
 public data class RankDescriptions(
     /**
      * Rank S description.