chore(storybook): consolidate storybook and enhance plugin stories (#37771)

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

superset-frontend/plugins/plugin-chart-echarts/src/Timeseries/stories/stackWithNulls.ts

@@ -0,0 +1,36 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+export default [
+  {
+    ds: 1293840000000,
+    '1': 2,
+    '2': 1,
+  },
+  {
+    ds: 1325376000000,
+    '1': null,
+    '2': null,
+  },
+  {
+    ds: 1356998400000,
+    '1': null,
+    '2': 1,
+  },
+];