data: entity: Add json factory

Will be used to facilitate backup-restore functionality
Issue: #41

lib/data/repository/booru/entity/post.dart

@@ -30,5 +30,7 @@ class Post with _$Post {
     @HiveField(19, defaultValue: []) @Default([]) List<String> tagsMeta,
   }) = _Post;
 
+  factory Post.fromJson(Map<String, dynamic> json) => _$PostFromJson(json);
+
   static const empty = Post();
 }

lib/data/repository/favorite_post/entity/favorite_post.dart

@@ -1,19 +1,21 @@
 import 'package:boorusphere/data/repository/booru/entity/post.dart';
+import 'package:freezed_annotation/freezed_annotation.dart';
 import 'package:hive/hive.dart';
 
+part 'favorite_post.freezed.dart';
 part 'favorite_post.g.dart';
 
-@HiveType(typeId: 5, adapterName: 'FavoritePostAdapter')
-class FavoritePost {
-  const FavoritePost({
-    this.post = Post.empty,
-    this.timestamp = 0,
-  });
+@freezed
+class FavoritePost with _$FavoritePost {
+  @HiveType(typeId: 5, adapterName: 'FavoritePostAdapter')
+  const factory FavoritePost({
+    @HiveField(0, defaultValue: Post.empty) @Default(Post.empty) Post post,
+    @HiveField(1, defaultValue: 0) @Default(0) int timestamp,
+  }) = _FavoritePost;
+  const FavoritePost._();
 
-  @HiveField(0, defaultValue: Post.empty)
-  final Post post;
-  @HiveField(1, defaultValue: 0)
-  final int timestamp;
+  factory FavoritePost.fromJson(Map<String, dynamic> json) =>
+      _$FavoritePostFromJson(json);
 
   String get key => '${post.id}@${post.serverId}';
 }

lib/data/repository/search_history/entity/search_history.dart

@@ -12,4 +12,6 @@ class SearchHistory with _$SearchHistory {
     @HiveField(0, defaultValue: '') @Default('*') String query,
     @HiveField(1, defaultValue: '') @Default('') String server,
   }) = _SearchHistory;
+  factory SearchHistory.fromJson(Map<String, dynamic> json) =>
+      _$SearchHistoryFromJson(json);
 }