feat: add quick select algorithm and test #6

[prisojacques]

QuickSelect is an efficient algorithm for finding the kth smallest element in an unsorted array. It uses a partitioning technique similar to QuickSort to divide the array and narrow down the search range. With an average time complexity of O(n), QuickSelect is a powerful tool for retrieving specific elements without sorting the entire array.

[appgurueu]

How can you speak of a "worst case" and a "best case" when your QuickSelect is randomized? Whether partition splits evenly will depend on the random pivot which is chosen rather than the order of the array.

Please just generate a few random arrays, QuickSelect a few items, then sort the array and compare the results.

Side note: Your description feels like it was written by ChatGPT. Please do not dump chatbot spam on us. If it was written by you, please be aware that you don't need to add a completely redundant explanation of what the code does in the PR; what the code does should be clear from the code through good variable naming and comments.