nzb-postproc 0.2.3

Post-processing pipeline: par2 verify/repair, RAR/7z/ZIP extraction, cleanup.

This crate contains:

• detect — File detection helpers (par2, RAR, 7z, ZIP, cleanup candidates)
• par2 — Native PAR2 verify/repair via rust-par2
• unpack — RAR extraction (unrar), 7z (7z binary), ZIP (zip crate)
• pipeline — Orchestrate: verify -> repair -> extract -> cleanup