List product variant serials

curl --request GET \
  --url https://api.shoppex.io/dev/v1/products/{id}/variants/{variantId}/serials \
  --header 'Authorization: Bearer <token>'

{
  "data": [
    {
      "id": "serial_1",
      "serial": "ABC-123",
      "variant_id": "variant_1",
      "variant_title": "Gold",
      "created_at": "2026-03-15T12:00:00.000Z"
    }
  ],
  "pagination": {
    "total": 21,
    "page": 2,
    "limit": 10,
    "total_pages": 3,
    "has_more": true
  }
}