Add rust extension

ext/mcp/src/lib.rs

@@ -0,0 +1,12 @@
+use magnus::{function, Error, Ruby};
+
+fn distance(a: (f64, f64), b: (f64, f64)) -> f64 {
+    ((b.0 - a.0).powi(2) + (b.1 - a.1).powi(2)).sqrt()
+}
+
+#[magnus::init]
+fn init(ruby: &Ruby) -> Result<(), Error> {
+    ruby.define_global_function("distance", function!(distance, 2));
+
+    Ok(())
+}