Initial commit: xenia-rs workspace for Xbox 360 RE

Rust reimplementation of the xenia Xbox 360 emulator targeting reverse-
engineering and preservation, initially scoped to Project Sylpheed.

Includes:
- XEX2 loader (LZX decompression, AES decryption, PE parsing)
- XISO / XGD2 disc image VFS
- PPC interpreter with 200+ opcodes and VMX128 decoding
- Static analyzer: functions, cross-references, labels, asm + SQLite output
- HLE kernel covering the xboxkrnl/xam subset used by Sylpheed init
- Debugger with in-memory and SQLite-backed execution tracing
- `xenia-rs` CLI with extract/dis/exec commands that produce cumulative,
  superset SQLite databases and opt-in instruction/import/branch traces

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

crates/xenia-memory/src/mmio.rs

@@ -0,0 +1,27 @@
+/// Represents a mapped MMIO region with read/write callbacks.
+/// Instead of trapping access violations (as the C++ JIT does), the interpreter
+/// explicitly checks each memory access against registered MMIO regions.
+pub struct MmioRegion {
+    pub base_address: u32,
+    pub mask: u32,
+    pub size: u32,
+    pub read_callback: Box<dyn Fn(u32) -> u32 + Send + Sync>,
+    pub write_callback: Box<dyn Fn(u32, u32) + Send + Sync>,
+}
+
+impl MmioRegion {
+    pub fn contains(&self, addr: u32) -> bool {
+        let masked = addr & self.mask;
+        masked >= self.base_address && masked < self.base_address + self.size
+    }
+}
+
+impl std::fmt::Debug for MmioRegion {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("MmioRegion")
+            .field("base_address", &format_args!("{:#010x}", self.base_address))
+            .field("mask", &format_args!("{:#010x}", self.mask))
+            .field("size", &format_args!("{:#x}", self.size))
+            .finish()
+    }
+}