Goal: Given an array of unique elements, return all possible subsequences. A subsequence is a sequence that can be derived from an array by deleting some or no elements without changing the order of the remaining elements. For example: Source challenge: https://github.com/type-challenges/type-challenges/tree/main/questions/08987-medium-subsequence Reference explanation: https://github.com/ghaiklor/type-challenges-solutions/blob/main/en/medium-subsequence.md