Separate test and example for Irisawa hexlet

Put shared code in the conditionally compiled `engine::irisawa` module.

app-proto/examples/irisawa-hexlet.rs

@@ -0,0 +1,25 @@
+use dyna3::engine::{Q, irisawa::realize_irisawa_hexlet};
+
+fn main() {
+    const SCALED_TOL: f64 = 1.0e-12;
+    let (config, success, history) = realize_irisawa_hexlet(SCALED_TOL);
+    print!("\nCompleted Gram matrix:{}", config.tr_mul(&*Q) * &config);
+    if success {
+        println!("Target accuracy achieved!");
+    } else {
+        println!("Failed to reach target accuracy");
+    }
+    println!("Steps: {}", history.scaled_loss.len() - 1);
+    println!("Loss: {}", history.scaled_loss.last().unwrap());
+    if success {
+        println!("\nChain diameters:");
+        println!("  {} sun (given)", 1.0 / config[(3, 3)]);
+        for k in 4..9 {
+            println!("  {} sun", 1.0 / config[(3, k)]);
+        }
+    }
+    println!("\nStep │ Loss\n─────┼────────────────────────────────");
+    for (step, scaled_loss) in history.scaled_loss.into_iter().enumerate() {
+        println!("{:<4} │ {}", step, scaled_loss);
+    }
+}