feat support default Timer::Ptr = nullptr

src/sled/timer/timer.h

@@ -17,16 +17,17 @@ typedef uint32_t TimerGeneration;
 class Timer;
 
 struct TimerThreadDeleter {
+    TimerThreadDeleter() = default;
     TimerThreadDeleter(TaskQueueBase *owner);
     inline void operator()(Timer *timer);
 
 private:
-    TaskQueueBase *owner_;
+    TaskQueueBase *owner_ = nullptr;
 };
 
 class Timer {
 public:
-    using Ptr= std::unique_ptr<Timer, TimerThreadDeleter>;
+    using Ptr = std::unique_ptr<Timer, TimerThreadDeleter>;
 
     using OnExpired                 = std::function<sled::optional<DurationMs>()>;
     Timer(const Timer &)            = delete;