Add True Shot Ammo (Shopify JSON), Palmetto State Armory (Magento HTML),
Bulk Ammo (Magento HTML), and Natchez Shooters Supply (GraphQL API).
Extends scraper infrastructure with HttpClient.post_json/3 and an
optional fetch/2 callback on the Scraper behaviour for scrapers that
need custom HTTP flows (e.g. GraphQL POST requests).
