Add support for RPC V2 (#1087)

See this pull request for more info about what this does and how rpc v2
works: livekit/client-sdk-js#1832

Also, for an in depth description of behavior in edge cases, see
[RPC_SPEC.md
here](https://github.com/livekit/client-sdk-js/blob/00e93de0c3d85f846fa6707749fa46457a653a29/RPC_SPEC.md).

> [!WARNING]
> This pull request was LLM generated and has only been lightly reviewed
by the author, who is not a flutter expert. I have tested this and can
confirm it works in the happy path, but no other validation has been
done.
> 
> A more thorough review of this needs to occur before it could be
merged.

---------

Co-authored-by: Hiroshi Horie <548776+hiroshihorie@users.noreply.github.com>

Author: 1egoman

.changes/add-rpc-v2

@@ -0,0 +1 @@
+minor type="added" "Add RPC v2 (data-stream-based payloads) with v1 fallback"

example/lib/widgets/controls.dart

@@ -10,6 +10,7 @@ import 'package:livekit_client/livekit_client.dart';
 import 'package:flutter_webrtc/flutter_webrtc.dart';
 
 import '../exts.dart';
+import 'rpc_test_sheet.dart';
 
 class ControlsWidget extends StatefulWidget {
   //
@@ -38,6 +39,8 @@ class _ControlsWidgetState extends State<ControlsWidget> {
 
   bool _speakerphoneOn = AudioManager.instance.isSpeakerOutputPreferred;
 
+  final _rpcController = RpcTestController();
+
   @override
   void initState() {
     super.initState();
@@ -52,6 +55,7 @@ class _ControlsWidgetState extends State<ControlsWidget> {
   void dispose() {
     unawaited(_subscription?.cancel());
     participant.removeListener(_onChange);
+    _rpcController.dispose();
     super.dispose();
   }
 
@@ -459,8 +463,17 @@ class _ControlsWidgetState extends State<ControlsWidget> {
             icon: const Icon(Icons.bug_report),
             tooltip: 'Simulate scenario',
           ),
+          IconButton(
+            onPressed: _onTapRpcTest,
+            icon: const Icon(Icons.swap_horiz),
+            tooltip: 'RPC test',
+          ),
         ],
       ),
     );
   }
+
+  void _onTapRpcTest() {
+    unawaited(showRpcTestSheet(context, widget.room, _rpcController));
+  }
 }