[board] Write test_position!({starting,empty}) macros

These produce starting and empty positions, respectively, and then print the
position.

board/src/macros.rs

@@ -28,4 +28,18 @@ macro_rules! test_position {
             pos
         }
     };
+    (empty) => {
+        {
+            let pos = Position::empty();
+            println!("{pos}");
+            pos
+        }
+    };
+    (starting) => {
+        {
+            let pos = Position::starting();
+            println!("{pos}");
+            pos
+        }
+    };
 }