Sorting and two pointers

Implement Prototype(weights []int, target int) *Pair by testing all distinct positions. Solve sorts a copy and moves two pointers, O(n log n) time and O(n) copy space. Return the lexicographically smallest ascending value pair summing to target, or nil. Duplicates need distinct positions. Negative values are valid; arithmetic fits int. Preserve caller order.

Edit exercise.go; retain the public types and signatures. prototype and final are separate stages. The executable tests recover panics as failures, report named checks, and exit nonzero on any failure. A successful run must execute at least one check. Tests use logical time or explicit synchronization where relevant.