Switching compression algorithm from bzip2 to zstd

[auroraanna]

I noticed that unpacking the linux game download is very slow. I ran the extracted folder through tar and zstd and it is so much faster to unpack, even on higher compression levels like e.g. 12, while also not being bigger than the bzip2 file.

zstd is the compression algorithm you want for most things nowadays, it even ships in browsers alongside brotli, gzip and deflate.

[qreeves]

I'd need confirmation that this has become standard on all operating systems before switching. We technically target very old versions of Ubuntu/Debian as a baseline for compatibility purposes (and also our CI servers).