Allow Round() callers to choose the midpoint rounding mode

Allow callers of Maths.Round() and Double.Round() to choose whether midpoint values use ties-to-even or ties-away-from-zero rounding.

The rounding mode is optional. Existing calls such as value.Round(), value.Round(2), Maths.Round(value), and Maths.Round(value, 2) continue to work unchanged and retain ties-to-even as the default. Callers that need another policy can explicitly select AwayFromZero, including when rounding to negative decimal places.

This enables compatibility with external systems that require ties-away-from-zero while preserving Objo’s simple default API and current behaviour.