deps: add bzip2-rs for bz2 orig tarballs

Decode-only pure-Rust bzip2, matching flate2's pure-Rust default: no
new system packages for building pkh, and the archive-side origin of
the need is the busybox class of '.tar.bz2' upstream tarballs.

Cargo.toml

@@ -41,6 +41,7 @@ lazy_static = "1.4.0"
 unicode-width = "0.2"
 parking_lot = "0.12"
 suppaftp = "12"
+bzip2-rs = "0.1.2"
 
 [dev-dependencies]
 test-log = "0.2.19"