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/tests/pak_idxd_disc.rs

@@ -0,0 +1,99 @@
+//! Integration tests against the real extracted Project Sylpheed disc.
+//!
+//! These are **skipped** (pass as no-ops) when the extracted disc is not present,
+//! so the suite still runs on machines/CI without the game. Point at the disc via
+//! the `SYLPHEED_DISC` env var, or drop it at the default dev path below.
+
+use std::path::{Path, PathBuf};
+
+use sylpheed_formats::{IdxdObject, PakArchive};
+
+/// Locate the extracted disc root, or `None` to skip.
+fn disc_root() -> Option<PathBuf> {
+    if let Ok(p) = std::env::var("SYLPHEED_DISC") {
+        let p = PathBuf::from(p);
+        if p.join("dat").is_dir() {
+            return Some(p);
+        }
+    }
+    let default = Path::new(
+        "/home/fabi/RE - Project Sylpheed/Project Sylpheed - Arc of Deception (USA, Europe) (En,Ja)",
+    );
+    if default.join("dat").is_dir() {
+        return Some(default.to_path_buf());
+    }
+    None
+}
+
+macro_rules! skip_without_disc {
+    ($root:ident) => {
+        let Some($root) = disc_root() else {
+            eprintln!("SKIP: extracted disc not found (set SYLPHEED_DISC to enable)");
+            return;
+        };
+    };
+}
+
+#[test]
+fn deftables_header_and_first_entry() {
+    skip_without_disc!(root);
+    let arc = PakArchive::open(root.join("hidden/DefTables.pak")).unwrap();
+    assert_eq!(arc.len(), 1465);
+    assert_eq!(arc.block_size, 0x800);
+    assert_eq!(arc.flags, 0x1000_0000);
+    // TOC is sorted ascending by name_hash.
+    assert!(arc
+        .entries()
+        .windows(2)
+        .all(|w| w[0].name_hash < w[1].name_hash));
+    // First entries decompress to a known inner format (IDXD or XML).
+    let first = &arc.entries()[0];
+    let payload = arc.read(first).unwrap();
+    assert!(
+        payload.starts_with(b"IDXD") || payload.starts_with(b"<?xml"),
+        "unexpected inner magic: {:?}",
+        &payload[..4.min(payload.len())]
+    );
+}
+
+#[test]
+fn deltasaber_craft_stats() {
+    skip_without_disc!(root);
+    let arc = PakArchive::open(root.join("dat/GP_MAIN_GAME_E.pak")).unwrap();
+    // rou_f001 "DeltaSaber" — the player craft. Entry hash discovered via content scan.
+    let bytes = arc.read_by_hash(0x7c96_296c).expect("entry present").unwrap();
+    let obj = IdxdObject::parse(&bytes).unwrap();
+    // identifier-valued fields via get_raw
+    assert_eq!(obj.get_raw("Type"), Some("Craft"));
+    assert_eq!(obj.get_raw("Model"), Some("rou_f001"));
+    // numeric flight/combat constants via the reliable typed getters
+    assert_eq!(obj.get_f32("Size_X"), Some(10.0));
+    assert_eq!(obj.get_f32("Size_Y"), Some(7.0));
+    assert_eq!(obj.get_f32("Size_Z"), Some(29.0));
+    assert_eq!(obj.get_f32("HP"), Some(1000.0)); // now bound (robust pool start)
+    assert_eq!(obj.get_f32("MinimumVelocity"), Some(100.0));
+    assert_eq!(obj.get_f32("MaximumVelocity"), Some(1200.0));
+    assert_eq!(obj.get_f32("CruisingVelocity"), Some(700.0));
+    assert_eq!(obj.get_f32("Acceleration"), Some(600.0));
+    assert_eq!(obj.get_f32("Deceleration"), Some(400.0));
+    assert_eq!(obj.get_i64("Turn_AngularVelocity"), Some(100));
+    assert_eq!(obj.get_f32("ChargeSpeed"), Some(800.0));
+    assert_eq!(obj.get_f32("RadarRange"), Some(500000.0));
+    // a defaulted/omitted field must be None, not a neighbouring key
+    assert_eq!(obj.get_f32("ShieldRatio"), None);
+}
+
+#[test]
+fn dsaber_missile_weapon_stats() {
+    skip_without_disc!(root);
+    let arc = PakArchive::open(root.join("dat/GP_MAIN_GAME_E.pak")).unwrap();
+    // Weapon_DSaber_P_wep_26_Missile
+    let bytes = arc.read_by_hash(0x4666_5408).expect("entry present").unwrap();
+    let obj = IdxdObject::parse(&bytes).unwrap();
+    assert_eq!(obj.get_str("TargetType"), Some("Vessel,Craft"));
+    assert_eq!(obj.get_i64("LoadingCount"), Some(144));
+    assert_eq!(obj.get_f32("Interval"), Some(3.00));
+    assert_eq!(obj.get_f32("Mass"), Some(0.77));
+    assert_eq!(obj.get_i64("TriggerShotCount"), Some(12));
+    assert_eq!(obj.get_f32("MaximumRange"), Some(10000.0));
+}