Support trace files compressed by Zstandard (.zst)

[tatsuya6502]

Support directly reading a trace file compressed by Zstandard (.zst). We can use ruzstd, a pure Rust implementation of Zstandard decompressor.

Background

I created a repository and put the ARC trace files there. I did it because the original files are no longer available for download (#12).

When I put them, I compressed them using Zstandard to save storage space. It will be convenient if mokabench can read them without decompressing by hands.