feat: add AES-128-CBC decryption and clap CLI (M4)

Add session key derivation and payload decryption using AES-128-CBC
with well-known XEX2 master keys. Refactor CLI to use clap with
inspect/extract subcommands. Extend FileFormatInfo to parse
compression metadata (basic blocks, LZX window size/block chain).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/lib.rs

@@ -6,6 +6,7 @@
 //! provides types and functions to parse the binary format and extract
 //! structured information from XEX2 files.
 
+pub mod crypto;
 pub mod display;
 pub mod error;
 pub mod header;