Add support for Zstandard compression

[cs-util]

Complete the started https://github.com/cs-util-com/cscore/tree/feature/zstdCompression branch to add support for the Zstd compression format via the Zstandard library ( https://www.nuget.org/packages/ZstdSharp.Port )

The pure xunit test works correctly but the library is not usable in Unity yet