Function mod

mod(n: number, m: number): number
Computes the true mathematical modulo of two JS standard numbers, ensuring a non-negative result.
Parameters
- n: number
  The dividend.
- m: number
  The divisor (must be a positive, non-zero number).
Returns number
The positive remainder representing n mod m.
Remarks
In standard JavaScript, the % operator computes the remainder, which can result in a negative number if the dividend n is negative. This helper function corrects that behavior to return a mathematically sound positive modulo in the range [0, m).
Example
```
mod(5, 3);   // returns 2
mod(-1, 3);  // returns 2 (whereas -1 % 3 returns -1)
```
- Defined in src/helpers.ts:135