#1698 Unpacking support for zstd 7z archives made by alternative 7z archiver

[Tish]

Hey!

I know it's not standard, but since 7z fork exists which brings in other compression methods via plugin system, I'd like to see just decompressing support in main 7z software. Would that be possible? zstd is the one that already has support, but only in ZIP archives. At least for zst, as it's the one I get mostly.

Could it be done, please?