Fixing namespace naming to be consistent

src/darwin/Framework/CHIP/MTRBaseDevice.mm

@@ -62,7 +62,7 @@
 using chip::Optional;
 using chip::SessionHandle;
 using chip::Messaging::ExchangeManager;
-using namespace chip::Metrics::DarwinFramework;
+using namespace chip::Tracing::DarwinFramework;
 
 NSString * const MTRAttributePathKey = @"attributePath";
 NSString * const MTRCommandPathKey = @"commandPath";

src/darwin/Framework/CHIP/MTRDeviceController.mm

@@ -107,7 +107,7 @@
 typedef id (^SyncWorkQueueBlockWithReturnValue)(void);
 typedef BOOL (^SyncWorkQueueBlockWithBoolReturnValue)(void);
 
-using namespace chip::Metrics::DarwinFramework;
+using namespace chip::Tracing::DarwinFramework;
 
 @implementation MTRDeviceController {
     // Atomic because it can be touched from multiple threads.

src/darwin/Framework/CHIP/MTRDeviceControllerDelegateBridge.mm

@@ -23,7 +23,7 @@
 #import "MTRMetricKeys.h"
 #import "MTRMetricsCollector.h"
 
-using namespace chip::Metrics::DarwinFramework;
+using namespace chip::Tracing::DarwinFramework;
 
 MTRDeviceControllerDelegateBridge::MTRDeviceControllerDelegateBridge(void)
     : mDelegate(nil)

src/darwin/Framework/CHIP/MTRMetricKeys.h

@@ -18,7 +18,7 @@
 #include <tracing/metric_event.h>
 
 namespace chip {
-namespace Metrics {
+namespace Tracing {
 namespace DarwinFramework {
 
 constexpr Tracing::MetricKey kMetricDeviceCommissioning = "dwnfw_device_commissioning";