Refactored code as per review comments

lib/src/platform/src/realtime/connection.dart

@@ -40,6 +40,11 @@ class Connection extends PlatformObject {
   /// member.
   String? id;
 
+  /// fetchId returns unique public identifier for this connection.
+  /// used to identify this member.
+  Future<String?> fetchId() =>
+      invoke<String?>(PlatformMethod.connectionId);
+
   /// A unique private connection key used to recover or resume a connection,
   /// assigned by Ably.
   ///
@@ -49,7 +54,19 @@ class Connection extends PlatformObject {
   /// to publish on behalf of this client. See the
   /// [publishing over REST on behalf of a realtime client docs](https://ably.com/docs/rest/channels#publish-on-behalf)
   /// for more info.
-  Future<String?> get key => invoke<String?>(PlatformMethod.connectionKey);
+  String? key;
+
+  /// fetchKey returns a unique private connection key used to recover
+  /// or resume a connection, assigned by Ably.
+  ///
+  /// When recovering a connection explicitly, the `recoveryKey` is used in the
+  /// recover client options as it contains both the key and the last message
+  /// serial. This private connection key can also be used by other REST clients
+  /// to publish on behalf of this client. See the
+  /// [publishing over REST on behalf of a realtime client docs](https://ably.com/docs/rest/channels#publish-on-behalf)
+  /// for more info.
+  Future<String?> fetchKey() =>
+      invoke<String?>(PlatformMethod.connectionKey);
 
   /// The recovery key string can be used by another client to recover this
   /// connection's state in the recover client options property.