Use a common macro to instrument each part

crates/common/src/lib.rs

@@ -0,0 +1,14 @@
+use std::time::Instant;
+
+#[macro_export]
+macro_rules! instrument {
+    ($part1:expr, $part2:expr) => {
+        let mut now = Instant::now();
+        println!("Part 1: {}", $part1);
+        println!("(elapsed: {:?})", now.elapsed());
+        now = Instant::now();
+        println!("");
+        println!("Part 2: {}", $part2);
+        println!("(elapsed: {:?})", now.elapsed());
+    };
+}