DepthPrecision: string & { __brand: "DepthPrecision" }

Validated depth precision for order book subscriptions.

Created via depthPrecision from a user-facing level (1–18). Level 1 = most precise (finest tick), 18 = most grouped.

Required by O2WebSocket.streamDepth. The high-level O2Client.streamDepth accepts a plain number and creates this internally.