feat: Implement workflow form handling for paused workflows

- Added module-level storage for pending forms to manage state across sessions.
- Introduced functions to set, get, and clear pending forms with expiration handling.
- Enhanced DifyServiceAPIRunner to support resuming paused workflows via form actions.
- Implemented logic to yield human input requests and display appropriate messages.
- Updated workflow submission methods to handle paused states and resume actions.
- Ensured proper merging of pending form actions with user inputs for seamless interaction.

src/langbot/pkg/pipeline/respback/respback.py

@@ -40,7 +40,7 @@ class SendResponseBackStage(stage.PipelineStage):
         has_chunks = any(isinstance(msg, provider_message.MessageChunk) for msg in query.resp_messages)
         # TODO 命令与流式的兼容性问题
         if await query.adapter.is_stream_output_supported() and has_chunks:
-            is_final = [msg.is_final for msg in query.resp_messages][0]
+            is_final = [msg.is_final for msg in query.resp_messages][-1]
             await query.adapter.reply_message_chunk(
                 message_source=query.message_event,
                 bot_message=query.resp_messages[-1],