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/pipelinemgr.py

@@ -157,7 +157,7 @@ class RuntimePipeline:
                     bot_message=query.resp_messages[-1],
                     message=result.user_notice,
                     quote_origin=query.pipeline_config['output']['misc']['quote-origin'],
-                    is_final=[msg.is_final for msg in query.resp_messages][0],
+                    is_final=[msg.is_final for msg in query.resp_messages][-1],
                 )
             else:
                 await query.adapter.reply_message(