manage products and variants with the bigcommerce catalog api including rate limits

Steps

1. Authenticate by including `X-Auth-Token` header with your store API token and target `https://api.bigcommerce.com/stores/{store_hash}/v3/catalog/products` for all catalog operations.
2. Create a product by POSTing to the products endpoint with required fields: `name`, `type` (`physical` or `digital`), `weight`, and `price`; the response returns the new product's `id`.
3. Add variants by POSTing to `/products/{product_id}/variants` with `option_values` (array of option value IDs) and variant-specific fields like `price`, `sku`, and `inventory_level`.
4. Update a product or variant with a PUT request to the respective resource endpoint using the numeric ID; only include fields you want to change (partial updates are supported).
5. Monitor rate limit headers in every response: `X-Rate-Limit-Requests-Left`, `X-Rate-Limit-Time-Reset-Ms`, and `X-Rate-Limit-Requests-Quota` to dynamically throttle your request pace.
6. When rate limited (HTTP 429), back off for the duration indicated in `X-Rate-Limit-Time-Reset-Ms` before retrying.