Initial project setup

Scaffold xex2tractor Rust project with cargo, add MIT license, README,
and XEX2 file format documentation.

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

src/main.rs

@@ -0,0 +1,3 @@
+fn main() {
+    println!("Hello, world!");
+}