Function calculatePercentageChange

calculatePercentageChange(oldValue: Decimal, newValue: Decimal): Decimal
Calculate percentage change between two values.
Parameters
- oldValue: Decimal
  The original value
- newValue: Decimal
  The new value
Returns Decimal
The percentage change as a Decimal
Example
```
const pnlPercent = calculatePercentageChange(
  toDecimal("100"),  // original
  toDecimal("120")   // current
); // 20 (representing 20%)
```
- Defined in packages/trading/src/utils/decimal.ts:156