Serialization fixes

core/src/main/kotlin/com/insanusmokrassar/postssystem/core/content/Content.kt

@@ -7,6 +7,7 @@ typealias ContentId = String
 /**
  * Content which is planned to be registered in database
  */
+@Serializable
 sealed class Content
 
 @Serializable
@@ -24,6 +25,7 @@ data class SimpleTextContent(
  * [com.insanusmokrassar.postssystem.core.post.RegisteredPost]s by using
  * [com.insanusmokrassar.postssystem.core.post.api.ReadPostsAPI.getPostsByContent]
  */
+@Serializable
 data class RegisteredContent(
     val id: ContentId,
     val content: Content

core/src/main/kotlin/com/insanusmokrassar/postssystem/core/utils/pagination/PaginationResult.kt

@@ -1,10 +1,13 @@
 package com.insanusmokrassar.postssystem.core.utils.pagination
 
+import kotlinx.serialization.Serializable
+
+@Serializable
 data class PaginationResult<T>(
     override val page: Int,
     val pagesNumber: Int,
     val results: List<T>,
-    override val size: Int = results.size
+    override val size: Int
 ) : Pagination
 
 fun <T> Pagination.createResult(