chore(frontend): comprehensive TypeScript quality improvements (#37625)

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

superset-frontend/plugins/plugin-chart-echarts/src/BigNumber/BigNumberViz.tsx

@@ -192,8 +192,19 @@ function BigNumberVis({
 
   const renderHeader = (maxHeight: number) => {
     const { bigNumber, width, colorThresholdFormatters, onContextMenu } = props;
-    // @ts-ignore
-    const text = bigNumber === null ? t('No data') : headerFormatter(bigNumber);
+    // Format bigNumber based on its type: null/undefined -> "No data", number -> format, else -> string
+    let text: string;
+    if (bigNumber === null || bigNumber === undefined) {
+      text = t('No data');
+    } else if (typeof bigNumber === 'number') {
+      text = headerFormatter(bigNumber);
+    } else {
+      // For string/boolean/Date values, convert to number if possible, else show as string
+      const numValue = Number(bigNumber);
+      text = Number.isNaN(numValue)
+        ? String(bigNumber)
+        : headerFormatter(numValue);
+    }
 
     const hasThresholdColorFormatter =
       Array.isArray(colorThresholdFormatters) &&

superset-frontend/plugins/plugin-chart-echarts/src/BigNumber/BigNumberWithTrendline/transformProps.ts

@@ -215,10 +215,13 @@ export default function transformProps(
     }
   }
 
-  if (data.length > 0) {
-    const reversedData = [...sortedData].reverse();
-    // @ts-ignore
-    trendLineData = showTrendLine ? reversedData : undefined;
+  if (data.length > 0 && showTrendLine) {
+    // Filter out entries with null timestamps and reverse for chronological order
+    // TimeSeriesDatum requires [number, number | null] - timestamp must be non-null
+    const validData = sortedData.filter(
+      (d): d is [number, number | null] => d[0] !== null,
+    );
+    trendLineData = [...validData].reverse();
   }
 
   let className = '';
@@ -379,7 +382,7 @@ export default function transformProps(
     width,
     height,
     bigNumber,
-    // @ts-ignore
+    // @ts-expect-error
     bigNumberFallback,
     className,
     headerFormatter: yAxisFormatter,