feat: parse and display all optional headers (M2)

Implement parsing for all 15 optional header types found in XEX2 files:
inline values (entry point, base address, stack size, system flags),
fixed-size structures (execution info, file format, TLS, game ratings,
LAN key, checksum/timestamp), and variable-size structures (static
libraries, import libraries, resource info, original PE name, Xbox 360
logo). Add comprehensive unit and integration tests.

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

src/lib.rs

@@ -9,16 +9,20 @@
 pub mod display;
 pub mod error;
 pub mod header;
+pub mod optional;
 pub mod util;
 
 use error::Result;
 use header::Xex2Header;
+use optional::OptionalHeaders;
 
 /// A parsed XEX2 file containing all extracted structures.
 #[derive(Debug)]
 pub struct Xex2File {
     /// The main XEX2 header (magic, flags, sizes, offsets).
     pub header: Xex2Header,
+    /// All parsed optional headers.
+    pub optional_headers: OptionalHeaders,
 }
 
 /// Parses an XEX2 file from a byte slice.
@@ -27,6 +31,10 @@ pub struct Xex2File {
 /// Returns a [`Xex2File`] with all successfully parsed structures.
 pub fn parse(data: &[u8]) -> Result<Xex2File> {
     let header = header::parse_header(data)?;
+    let optional_headers = optional::parse_optional_headers(data, &header)?;
 
-    Ok(Xex2File { header })
+    Ok(Xex2File {
+        header,
+        optional_headers,
+    })
 }