feat: add toString method in ChannelStateChange class for improved debugging

It is used in chat logs

Author: ttypic

lib/src/main/java/io/ably/lib/realtime/ChannelStateListener.java

@@ -1,6 +1,7 @@
 package io.ably.lib.realtime;
 
 import io.ably.lib.types.ErrorInfo;
+import org.jetbrains.annotations.NotNull;
 
 /**
  * An interface whereby a client may be notified of state changes for a channel.
@@ -69,6 +70,17 @@ private ChannelStateChange(ErrorInfo reason, boolean resumed) {
         static ChannelStateChange createUpdateEvent(ErrorInfo reason, boolean resumed) {
             return new ChannelStateChange(reason, resumed);
         }
+
+        @Override
+        public @NotNull String toString() {
+            return '{' +
+                "event=" + event +
+                ", current=" + current +
+                ", previous=" + previous +
+                ", reason=" + reason +
+                ", resumed=" + resumed +
+                '}';
+        }
     }
 
     class Multicaster extends io.ably.lib.util.Multicaster<ChannelStateListener> implements ChannelStateListener {