Use pzstd instead of zstd
Should speed things up a little bit.
Partially done for decompression in 7458ea788f902dffcddca39fc2af3f2ba153dae6.
I wonder if we should just leave it this way. Were there any speed gains if you compress stuff with pzstd? (well, hypothetically it has to be faster, but is it? And by how much?)
Zstd decompression is already very fast, and often the extra speed provided by pzstd isn't necessary.
This is probably true in 2023, especially considering the consistent evolution of zstd. By the way, zstd itself already attempts to use multiple threads where possible. We may revert to zstd and measure the results.