Allow stopwatch and printcounter to go over 18 hours

Marlin/stopwatch.h

@@ -42,9 +42,9 @@ enum StopwatchState {
 class Stopwatch {
   private:
     StopwatchState state;
-    uint16_t accumulator;
-    uint32_t startTimestamp;
-    uint32_t stopTimestamp;
+    millis_t accumulator;
+    millis_t startTimestamp;
+    millis_t stopTimestamp;
 
   public:
     /**
@@ -101,7 +101,7 @@ class Stopwatch {
      * @details Returns the total number of seconds the timer has been running.
      * @return the delta since starting the stopwatch
      */
-    uint16_t duration();
+    millis_t duration();
 
     #if ENABLED(DEBUG_STOPWATCH)