NFT Alpha: OpenSea NFT market signals for an OpenSea collection slug. Body: { collection: string, collections?: string[] }. Returns listing/sale/bid counts, price stats, sell-through, and signals such as HIGH_DEMAND, UNDERPRICED_LISTING, BID_FRENZY, DUMP_WARNING, LOW_DEMAND. NFT Alpha OpenSea market signals for NFT listings, sales, bids, floor price, and bid frenzy. Not financial advice.