[Darwin] Followup PR for missed code review comments (#32447)

* [Darwin] Followup PR for missed code review comments

- Fixes following issues:  #32438, #32443, #32439

* Resytler fixes

* Address review comment

Author: anush-apple

src/darwin/Framework/CHIP/MTRMetrics.h

@@ -32,16 +32,17 @@ MTR_NEWLY_AVAILABLE
 @property (nonatomic, nullable, readonly, copy) NSNumber * value;
 
 /**
- * Error code for the metric data. This value when valid, holds the error code value
- * of the operation associated with the event.
+ * Error code for the metric data. This value, when not nil, holds the error code value
+ * of the operation associated with the event. Interpretation of the error code value
+ * dependents on the metric being emitted.
  */
 @property (nonatomic, nullable, readonly, copy) NSNumber * errorCode;
 
 /**
  * Duration of event associated with the metric. This value may be nil depending on
- * the event emitted.
+ * the event emitted. When not nil, the value of duration is of type NSTimeInterval.
  */
-@property (nonatomic, nullable, readonly, copy) NSNumber * durationMicroseconds;
+@property (nonatomic, nullable, readonly, copy) NSNumber * duration;
 
 @end
 

src/darwin/Framework/CHIP/MTRMetricsCollector.mm

@@ -80,16 +80,16 @@ - (instancetype)initWithMetricEvent:(const MetricEvent &)event
 - (void)setDurationFromMetricDataAndClearCounters:(MTRMetricData *)fromData
 {
     auto duration = _timePoint - fromData->_timePoint;
-    _durationMicroseconds = [NSNumber numberWithUnsignedLongLong:duration.count()];
+    _duration = [NSNumber numberWithDouble:double(duration.count()) / USEC_PER_SEC];
 
     // Clear timepoints to minimize history
     _timePoint = fromData->_timePoint = chip::System::Clock::Microseconds64(0);
 }
 
 - (NSString *)description
 {
-    return [NSString stringWithFormat:@"<MTRMetricData>: Type %d, Value = %@, Error Code = %@, Duration = %@ us",
-                     static_cast<int>(_type), self.value, self.errorCode, self.durationMicroseconds];
+    return [NSString stringWithFormat:@"<MTRMetricData: Type %d, Value = %@, Error Code = %@, Duration = %@ us>",
+                     static_cast<int>(_type), self.value, self.errorCode, self.duration];
 }
 
 @end