Support zstd-compressed ELF sections.

[khuey]

zstd has been introduced as an alternative to zlib for the compression of debug sections.[0] Toolchain support is widely present at this time but lack of support in backtrace is a severe limitation on using this feature in Rust programs.

This uses a Rust reimplementation of zstd (the ruzstd crate). This has the benefit of simplifying the build process, but this crate is less used and admittedly slower than the zstd crate that binds to the C libzstd.

[0] https://maskray.me/blog/2022-09-09-zstd-compressed-debug-sections