Add calculation for `get_trading_volume` to rust sdk

[DannyDelott]

Trading volume is only calculated in the ts sdk right now, but moving this to the sdk would create a single source of truth where volume is measured in bonds.

https://github.com/delvtech/hyperdrive-frontend/blob/main/packages/hyperdrive-js-core/src/hyperdrive/ReadHyperdrive/ReadHyperdrive.ts#L562-L588