feat: support every song difficulty including Easy and Normal

src/lib/engine/analysis-history.test.ts

@@ -41,6 +41,13 @@ test('성장 상태를 공유하는 기록 백업을 손실 없이 읽고 잘못
   const parsed = parseAnalysisArchive(JSON.stringify(archive));
   assert.equal(parsed.records.length, 2); assert.equal(parsed.snapshots.length, 1);
   assert.deepEqual(parsed.snapshots[0].growth, growth);
+  for (const difficulty of ['easy', 'normal', 'hard', 'expert']) {
+    record.settings.difficulty = difficulty;
+    assert.equal(parseAnalysisArchive(JSON.stringify(archive)).records[0].settings.difficulty, difficulty);
+  }
+  record.settings.difficulty = 'invalid';
+  assert.throws(() => parseAnalysisArchive(JSON.stringify(archive)));
+  record.settings.difficulty = 'expert';
   record.settings.awakenings[0] = 8;
   assert.throws(() => parseAnalysisArchive(JSON.stringify(archive)));
 });