Use store $ assignment to fix batch selection

Without the `=` sign, the reactivity chain were broken.
Using an assignment by prefixing the store with a `$` fixes this.

https://svelte.dev/docs#component-format-script-4-prefix-stores-with-$-to-access-their-values

src/DataTable/DataTable.svelte

@@ -195,16 +195,14 @@
   $: if (radio || batchSelection) selectable = true;
   $: tableSortable.set(sortable);
   $: headerKeys = headers.map(({ key }) => key);
-  $: tableRows.set(
+  $: $tableRows = rows.map((row) => ({
-    rows.map((row) => ({
     ...row,
     cells: headerKeys.map((key, index) => ({
       key,
       value: resolvePath(row, key),
       display: headers[index].display,
     })),
-    }))
+  }));
-  );
   $: sortedRows = [...$tableRows];
   $: ascending = $sortHeader.sortDirection === "ascending";
   $: sortKey = $sortHeader.key;