List every builder perp dex on Hyperliquid

Returns the active builder dex namespaces — `xyz` (XYZ), `flx` (Felix), `vntl` (Ventuals), `hyna` (HyENA), `km` (Kinetiq), `abcd`, `cash`, `para`. Cached 5 minutes. The discovery list comes from HL `perpDexs`, so newly-launched dexes appear automatically without a code change.