Make ReadClient::Callback non-movable

The purpose of this interface is be called polymorphically through a
pointer. Moving it will invalidate the original instance and is very
likely to be a bug.

Make this type non-movable; this will fail compilation if a derived
class is stored in an inappropriate container that moves its elements.

As an example, ClusterStateCache is also currently movable, but moving
it retains a pointer to the moved-from instance via mBufferedReader, so
any further usage is likely to result in a invalid memory access.

src/app/ClusterStateCache.h

@@ -71,6 +71,14 @@ class ClusterStateCache : protected ReadClient::Callback
     class Callback : public ReadClient::Callback
     {
     public:
+        Callback() = default;
+
+        // Callbacks are not expected to be copyable or movable.
+        Callback(const Callback&) = delete;
+        Callback(Callback&&) = delete;
+        Callback& operator=(const Callback&) = delete;
+        Callback& operator=(Callback&&) = delete;
+
         /*
          * Called anytime an attribute value has changed in the cache
          */
@@ -103,6 +111,11 @@ class ClusterStateCache : protected ReadClient::Callback
         mHighestReceivedEventNumber = highestReceivedEventNumber;
     }
 
+    ClusterStateCache(const ClusterStateCache&) = delete;
+    ClusterStateCache(ClusterStateCache&&) = delete;
+    ClusterStateCache& operator=(const ClusterStateCache&) = delete;
+    ClusterStateCache& operator=(ClusterStateCache&&) = delete;
+
     void SetHighestReceivedEventNumber(EventNumber highestReceivedEventNumber)
     {
         mHighestReceivedEventNumber.SetValue(highestReceivedEventNumber);

src/app/ReadClient.cpp

@@ -45,7 +45,6 @@ ReadClient::ReadClient(InteractionModelEngine * apImEngine, Messaging::ExchangeM
     mOnConnectionFailureCallback(HandleDeviceConnectionFailure, this)
 {
     mpExchangeMgr    = apExchangeMgr;
-    mpCallback       = apCallback;
     mInteractionType = aInteractionType;
 
     mpImEngine = apImEngine;

src/app/ReadClient.h

@@ -72,6 +72,14 @@ class ReadClient : public Messaging::ExchangeDelegate
     class Callback
     {
     public:
+        Callback() = default;
+
+        // Callbacks are not expected to be copyable or movable.
+        Callback(const Callback&) = delete;
+        Callback(Callback&&) = delete;
+        Callback& operator=(const Callback&) = delete;
+        Callback& operator=(Callback&&) = delete;
+
         virtual ~Callback() = default;
 
         /**