refactor: extract lib_timer

lib_timer/src/timer.cpp

@@ -0,0 +1,32 @@
+#include "timer.h"
+
+#include <chrono>
+
+Timer::Timer() { start(); };
+
+void Timer::start() { start_ = std::chrono::high_resolution_clock::now(); }
+
+void Timer::stop() { end_ = std::chrono::high_resolution_clock::now(); }
+
+long Timer::us() const {
+  return std::chrono::duration_cast<std::chrono::microseconds>(end_ - start_)
+      .count();
+}
+
+std::ostream &operator<<(std::ostream &os, const Timer &timer) {
+  long time = timer.us();
+
+  if (time >= 1e6) {
+    os << time / static_cast<long>(1e6) << " s ";
+    time %= static_cast<long>(1e6);
+  }
+
+  if (time >= 1e3) {
+    os << time / static_cast<long>(1e3) << " ms ";
+    time %= static_cast<long>(1e3);
+  }
+
+  os << time << " µs";
+
+  return os;
+}