refactor: extract lib_timer

lib_timer/include/timer.h

@@ -0,0 +1,20 @@
+#pragma once
+
+#include <chrono>
+#include <ostream>
+
+class Timer {
+private:
+  std::chrono::time_point<std::chrono::high_resolution_clock> start_;
+  std::chrono::time_point<std::chrono::high_resolution_clock> end_;
+
+public:
+  Timer();
+
+  void start();
+  void stop();
+
+  long us() const;
+};
+
+std::ostream &operator<<(std::ostream &os, const Timer &timer);