Function calculateValue

calculateValue(
    start: string | number | number[],
    end: string | number | number[],
    progress: number,
): string | number | number[] | undefined
Interpolate between two values (number, number[], or string) by progress.

Handles all RPE value types:
- Numbers: standard linear interpolation.
- number arrays (e.g. RGB color): per-component interpolation.
- Strings with %P% markers: interpolates the embedded number.
- Text reveal strings: reveals/hides characters progressively when one string is a prefix of the other.
- Other strings: returns start until progress >= 1, then end.
Parameters
- start: string | number | number[]
  Start value.
- end: string | number | number[]
  End value.
- progress: number
  Progress ∈ [0, 1].
Returns string | number | number[] | undefined
Interpolated value; type matches the input types.
Example
```
calculateValue(0, 255, 0.5);              // 127.5
calculateValue([255, 0, 0], [0, 0, 255], 0.5); // [127.5, 0, 127.5]
calculateValue('%P%0', '%P%100', 0.3);    // '30'
calculateValue('Hello', 'Hello World', 0.5); // 'Hello Wor'
```
- Defined in events.ts:230