raise MTRDevice for subclassing

src/darwin/Framework/CHIP/MTRDevice.mm

@@ -142,16 +142,6 @@ - (BOOL)callDelegateSynchronouslyWithBlock:(void (^)(id<MTRDeviceDelegate>))bloc
 #endif
 @end
 
-NSNumber * MTRClampedNumber(NSNumber * aNumber, NSNumber * min, NSNumber * max)
-{
-    if ([aNumber compare:min] == NSOrderedAscending) {
-        return min;
-    } else if ([aNumber compare:max] == NSOrderedDescending) {
-        return max;
-    }
-    return aNumber;
-}
-
 /* BEGIN DRAGONS: Note methods here cannot be renamed, and are used by private callers, do not rename, remove or modify behavior here */
 
 @interface NSObject (MatterPrivateForInternalDragonsDoNotFeed)
@@ -252,10 +242,6 @@ @implementation MTRDeviceClusterData {
     NSMutableDictionary<NSNumber *, MTRDeviceDataValueDictionary> * _attributes;
 }
 
-static NSString * const sDataVersionKey = @"dataVersion";
-static NSString * const sAttributesKey = @"attributes";
-static NSString * const sLastInitialSubscribeLatencyKey = @"lastInitialSubscribeLatency";
-
 - (void)storeValue:(MTRDeviceDataValueDictionary _Nullable)value forAttribute:(NSNumber *)attribute
 {
     _attributes[attribute] = value;
@@ -498,6 +484,15 @@ @implementation MTRDevice {
     NSMutableSet<MTRDeviceDelegateInfo *> * _delegates;
 }
 
+- (instancetype)initForSubclasses
+{
+    if (self = [super init]) {
+        // nothing, as superclass of MTRDevice is NSObject
+    }
+
+    return self;
+}
+
 - (instancetype)initWithNodeID:(NSNumber *)nodeID controller:(MTRDeviceController *)controller
 {
     if (self = [super init]) {

src/darwin/Framework/CHIP/MTRDevice_Concrete.h

@@ -0,0 +1,29 @@
+/**
+ *
+ *    Copyright (c) 2022-2023 Project CHIP Authors
+ *
+ *    Licensed under the Apache License, Version 2.0 (the "License");
+ *    you may not use this file except in compliance with the License.
+ *    You may obtain a copy of the License at
+ *
+ *        http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *    Unless required by applicable law or agreed to in writing, software
+ *    distributed under the License is distributed on an "AS IS" BASIS,
+ *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *    See the License for the specific language governing permissions and
+ *    limitations under the License.
+ */
+
+#import <Foundation/Foundation.h>
+#import <Matter/MTRDevice.h>
+
+NS_ASSUME_NONNULL_BEGIN
+
+@class MTRDeviceController;
+
+@interface MTRDevice_Concrete : MTRDevice
+
+@end
+
+NS_ASSUME_NONNULL_END