Mark / mid / 24h price snapshot for one spot pair
get
/v1/markets/hyperliquid/spot/pairs/{pair}Composite snapshot from HL `spotMetaAndAssetCtxs`. Cached 5s — hot endpoint. Unknown pair → 404 `unknown_pair`. `dayChangePct` is `(mark - prevDay) / prevDay * 100`; null when either is missing or prevDay is 0.