feat: implement new faster sort algorithm for Go 1.18

[aymanbagabas]

This implements the pdqsort algorithm for Go 1.18 and later. The new algorithm is ~10x faster than sort.Sort and was added to the slices package in Go 1.20.

The algorithm is backported from the stdlib and is used in this package to provide a faster median cut algorithm.

P.S. You can use my fork go get github.com/aymanbagabas/quant@master to use this patch