Filter data out into separate files

test/jouyou_kanji_test.dart

@@ -1,9 +1,9 @@
 import 'package:collection/collection.dart';
-import 'package:jadb/util/jouyou_kanji.dart';
+import 'package:jadb/const_data/kanji_grades.dart';
 import 'package:test/test.dart';
 
 void main() {
   test("Assert 2136 kanji in jouyou set", () {
-    expect(JOUYOU_KANJI.values.flattenedToSet.length, 2136);
+    expect(JOUYOU_KANJI_BY_GRADES.values.flattenedToSet.length, 2136);
   });
 }

test/search/kanji_search_test.dart

@@ -1,4 +1,4 @@
-import 'package:jadb/util/jouyou_kanji.dart';
+import 'package:jadb/const_data/kanji_grades.dart';
 import 'package:test/test.dart';
 
 import 'setup_database_connection.dart';
@@ -12,7 +12,7 @@ void main() {
   });
 
   group("Search all jouyou kanji", () {
-    JOUYOU_KANJI.forEach((grade, characters) {
+    JOUYOU_KANJI_BY_GRADES.forEach((grade, characters) {
       test("Search all kanji in grade $grade", () async {
         final connection = await setup_database_connection();