refactor: use method names for JSON-RPC dispatching (#932)

# Description

This PR changes the routing logic in the JsonRpcDispatcher, enforcing it
on the method name, rather that the object type.

Author: guglielmo-san

src/a2a/server/routes/jsonrpc_dispatcher.py

@@ -31,7 +31,6 @@
     DefaultServerCallContextBuilder,
     ServerCallContextBuilder,
 )
-from a2a.types import A2ARequest
 from a2a.types.a2a_pb2 import (
     AgentCard,
     CancelTaskRequest,
@@ -349,7 +348,7 @@ async def handle_requests(self, request: Request) -> Response:  # noqa: PLR0911,
             else:
                 try:
                     raw_result = await self._process_non_streaming_request(
-                        request_id, specific_request, call_context
+                        specific_request, call_context
                     )
                     handler_result = JSONRPC20Response(
                         result=raw_result, _id=request_id
@@ -385,7 +384,7 @@ async def handle_requests(self, request: Request) -> Response:  # noqa: PLR0911,
     async def _process_streaming_request(
         self,
         request_id: str | int | None,
-        request_obj: A2ARequest,
+        request_obj: Any,
         context: ServerCallContext,
     ) -> AsyncGenerator[dict[str, Any], None]:
         """Processes streaming requests (SendStreamingMessage or SubscribeToTask).
@@ -399,11 +398,12 @@ async def _process_streaming_request(
             An `AsyncGenerator` object to stream results to the client.
         """
         stream: AsyncGenerator | None = None
-        if isinstance(request_obj, SendMessageRequest):
+        method = context.state.get('method')
+        if method == 'SendStreamingMessage':
             stream = self.request_handler.on_message_send_stream(
                 request_obj, context
             )
-        elif isinstance(request_obj, SubscribeToTaskRequest):
+        elif method == 'SubscribeToTask':
             stream = self.request_handler.on_subscribe_to_task(
                 request_obj, context
             )
@@ -538,55 +538,53 @@ async def _handle_get_extended_agent_card(
     @validate_version(constants.PROTOCOL_VERSION_1_0)
     async def _process_non_streaming_request(  # noqa: PLR0911
         self,
-        request_id: str | int | None,
-        request_obj: A2ARequest,
+        request_obj: Any,
         context: ServerCallContext,
     ) -> dict[str, Any] | None:
-        """Processes non-streaming requests (message/send, tasks/get, tasks/cancel, tasks/pushNotificationConfig/*).
+        """Processes non-streaming requests.
 
         Args:
-            request_id: The ID of the request.
             request_obj: The proto request message.
             context: The ServerCallContext for the request.
 
         Returns:
             A dict containing the result or error.
         """
-        match request_obj:
-            case SendMessageRequest():
+        method = context.state.get('method')
+        match method:
+            case 'SendMessage':
                 return await self._handle_send_message(request_obj, context)
-            case CancelTaskRequest():
+            case 'CancelTask':
                 return await self._handle_cancel_task(request_obj, context)
-            case GetTaskRequest():
+            case 'GetTask':
                 return await self._handle_get_task(request_obj, context)
-            case ListTasksRequest():
+            case 'ListTasks':
                 return await self._handle_list_tasks(request_obj, context)
-            case TaskPushNotificationConfig():
+            case 'CreateTaskPushNotificationConfig':
                 return await self._handle_create_task_push_notification_config(
                     request_obj, context
                 )
-            case GetTaskPushNotificationConfigRequest():
+            case 'GetTaskPushNotificationConfig':
                 return await self._handle_get_task_push_notification_config(
                     request_obj, context
                 )
-            case ListTaskPushNotificationConfigsRequest():
+            case 'ListTaskPushNotificationConfigs':
                 return await self._handle_list_task_push_notification_configs(
                     request_obj, context
                 )
-            case DeleteTaskPushNotificationConfigRequest():
-                return await self._handle_delete_task_push_notification_config(
+            case 'DeleteTaskPushNotificationConfig':
+                await self._handle_delete_task_push_notification_config(
                     request_obj, context
                 )
-            case GetExtendedAgentCardRequest():
+                return None
+            case 'GetExtendedAgentCard':
                 return await self._handle_get_extended_agent_card(
                     request_obj, context
                 )
             case _:
-                logger.error(
-                    'Unhandled validated request type: %s', type(request_obj)
-                )
+                logger.error('Unhandled method: %s', method)
                 raise UnsupportedOperationError(
-                    message=f'Request type {type(request_obj).__name__} is unknown.'
+                    message=f'Method {method} is not supported.'
                 )
 
     def _create_response(