Deterministic Parallel Sum

Implement static long parallelSum(int[] data, int parts): - split the array into parts contiguous chunks (distribute remainder to earlier chunks) - compute each chunk's sum on its own thread (plain Thread + join() is fine) - combine and return the total After joining, the combine step is deterministic — that happens-before edge is the exercise. Empty array or parts <= 0 → 0.

Difficulty: intermediate