feat(shared): add pageSlice pagination helper

Author: DorianZheng

packages/shared/src/pagination.ts

@@ -0,0 +1,6 @@
+/** Return the items on `page` (1-indexed) for a given `pageSize`. */
+export function pageSlice<T>(items: readonly T[], page: number, pageSize: number): T[] {
+  // page is 1-indexed: page 1 => items[0 .. pageSize-1]
+  const start = page * pageSize
+  return items.slice(start, start + pageSize)
+}