Big thanks to @SciresM @sora10pls @Lusamine @architdate @ReignOfComputer for testing and contributing code / test cases. Can't add co-authors from the PR menu :(
Builds will fail because azure pipelines not yet updated with net6.
O(n) for speed & memory usage, as good as we can get.
Modified method is now less dumb. Array Copy doesn't have to worry about same-array overlapping src/dest regions