feat(formats): IPFB archive + IDXD definition readers

Add readers for Project Sylpheed's on-disc data format so the
reimplementation can load exact ship/weapon constants straight from
the game files.

- pak.rs: PakArchive — parse the IPFB `.pak` index + concatenated
  `.pNN` segments, binary-search the TOC by name-hash, and transparently
  inflate the per-entry "Z1" (zlib) container. Adds flate2.
- idxd.rs: IdxdObject — parse the IDXD reflective object serialization.
  The string pool stores properties value-before-key with defaulted
  fields omitted; typed getters (get_f32/get_i64/get_str/get_bool) read
  explicit values reliably, get_raw exposes identifier fields, and
  resolved_fields() enumerates every explicit (key,value). Defaulted
  fields correctly return None rather than a neighbouring key.
- sylpheed-cli: `pak list` (inventory entries + identity) and
  `pak dump <hash>` (full stat sheet for one object).

Verified against the real disc (auto-skipped without it): DeltaSaber
craft (HP=1000, Acceleration=600, velocity curve 100/700/1200, Turn=100,
RadarRange=500000) and the DSaber missile (LoadingCount=144, Interval=3.00,
Mass=0.77). 10 unit + 3 integration tests pass.

Not yet decoded: defaulted fields (many ratios, the *Count family) whose
values come from schema defaults or the hash-keyed binary node region.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

crates/sylpheed-formats/src/lib.rs

@@ -4,6 +4,7 @@
 //!
 //! This crate handles:
 //! - Reading game files from XISO disc images (native only)
+//! - Reading IPFB archives (`*.pak` / `*.pNN`) and the `IDXD` definition objects inside
 //! - Parsing Xbox 360 texture formats (XPR2 containers + DXT de-tiling)
 //! - Parsing mesh formats (to be reverse engineered)
 //! - Parsing audio formats (XMA → standard PCM)
@@ -15,6 +16,12 @@
 pub mod texture;
 pub mod vfs;
 
+// IPFB archive (`*.pak` index + `*.pNN` segments) reader
+pub mod pak;
+
+// IDXD reflective object (ship / weapon / effect / menu definitions) reader
+pub mod idxd;
+
 // XISO reading is not available in-browser
 #[cfg(not(target_arch = "wasm32"))]
 pub mod xiso;
@@ -26,5 +33,7 @@ pub mod mesh;
 pub mod audio;
 
 /// Re-export the most commonly used types at the crate root.
+pub use idxd::{IdxdError, IdxdObject};
+pub use pak::{PakArchive, PakEntry, PakError};
 pub use texture::{X360Texture, X360TextureFormat};
 pub use vfs::{GameAssets, VfsError};