Zstd labels, extensions, and option metadata.
This crate is part of the `use-archive` facade workspace. It describes zstd-related labels and options only. It does not compress, decompress, read zstd frames, or write zstd frames.
```rust
use use_zstd::{ZSTD_EXTENSION, ZstdOptions};
let options = ZstdOptions::default().with_level(3).with_checksum(true);
assert_eq!(ZSTD_EXTENSION, "zst");
assert_eq!(options.level, Some(3));
```