lib/search/kanji: make taughtIn into int?

lib/models/kanji_search/kanji_search_result.dart

@@ -7,7 +7,8 @@ class KanjiSearchResult extends Equatable {
   final String kanji;
 
   /// The school level that the kanji is taught in, if applicable.
-  final String? taughtIn;
+  /// Ranges from `1` to `10` (except 7)
+  final int? taughtIn;
 
   /// The lowest JLPT exam that this kanji is likely to appear in, if applicable.
   ///
@@ -121,10 +122,6 @@ class KanjiSearchResult extends Equatable {
         // 'kunyomiExamples': kunyomiExamples,
         'radical': radical?.toJson(),
         'parts': parts,
-        // 'strokeOrderDiagramUri': strokeOrderDiagramUri,
-        // 'strokeOrderSvgUri': strokeOrderSvgUri,
-        // 'strokeOrderGifUri': strokeOrderGifUri,
-        // 'uri': uri,
         'codepoints': codepoints,
         'nanori': nanori,
         'alternativeLanguageReadings': alternativeLanguageReadings,
@@ -136,7 +133,7 @@ class KanjiSearchResult extends Equatable {
   factory KanjiSearchResult.fromJson(Map<String, dynamic> json) {
     return KanjiSearchResult(
       kanji: json['kanji'] as String,
-      taughtIn: json['taughtIn'] as String?,
+      taughtIn: json['taughtIn'] as int?,
       jlptLevel: json['jlptLevel'] as String?,
       newspaperFrequencyRank: json['newspaperFrequencyRank'] as int?,
       strokeCount: json['strokeCount'] as int,