Add units to number widgets in the Stats.

ui/stats/NumberWidgetsList.tsx

@@ -22,14 +22,23 @@ const NumberWidgetsList = () => {
       gridGap={ 4 }
     >
       { isLoading ? skeletonElement :
-        numberWidgetsScheme.map(({ id, title }) =>
-          data?.counters[id] ? (
+        numberWidgetsScheme.map(({ id, title, formatFn }) => {
+          if (!data?.counters[id]) {
+            return null;
+          }
+
+          const value = formatNumberToMetricPrefix(Number(data.counters[id]));
+
+          return (
             <NumberWidget
               key={ id }
               label={ title }
-              value={ formatNumberToMetricPrefix(Number(data.counters[id])) }
+              value={ formatFn ?
+                formatFn(value) :
+                value }
             />
-          ) : null) }
+          );
+        }) }
     </Grid>
   );
 };

ui/stats/constants/number-widgets-scheme.ts

@@ -2,7 +2,7 @@ import type { Stats } from 'types/api/stats';
 
 type Key = keyof Stats['counters'];
 
-export const numberWidgetsScheme: Array<{id: Key; title: string}> = [
+export const numberWidgetsScheme: Array<{id: Key; title: string; formatFn?: (n: string) => string}> = [
   {
     id: 'totalBlocks',
     title: 'Total blocks',
@@ -10,6 +10,7 @@ export const numberWidgetsScheme: Array<{id: Key; title: string}> = [
   {
     id: 'averageBlockTime',
     title: 'Average block time',
+    formatFn: (n) => `${ n } s`,
   },
   {
     id: 'totalTransactions',