new: setting of termCursor type

lib/core/extension/enum.dart

@@ -0,0 +1,12 @@
+extension EnumListX<T> on List<T> {
+  T fromIndex(int index, [T? defaultValue]) {
+    try {
+      return this[index];
+    } catch (e) {
+      if (defaultValue != null) {
+        return defaultValue;
+      }
+      throw Exception('Invalid index: $index');
+    }
+  }
+}