Basic example from README broken

Copied all content from readme.
- greetings_worker.py
- greetings_workflow.py
- helloworld.py

Running server via docker-compose on latest main, although this doesn't matter since it's a client error.

Version 1.2.3. Python version 3.11.14.

```
❯ uv run helloworld.py
Traceback (most recent call last):
File "/home/discord/github.com/discord/discord/discord_hivemind/conductor/helloworld.py", line 36, in
main()
File "/home/discord/github.com/discord/discord/discord_hivemind/conductor/helloworld.py", line 21, in main
workflow = register_workflow(workflow_executor)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/discord/github.com/discord/discord/discord_hivemind/conductor/helloworld.py", line 10, in register_workflow
workflow.register(True)
File "/home/discord/github.com/discord/discord/discord_hivemind/.venv/lib/python3.11/site-packages/conductor/client/workflow/conductor_workflow.py", line 192, in register
workflow=self.to_workflow_def(),
^^^^^^^^^^^^^^^^^^^^^^
File "/home/discord/github.com/discord/discord/discord_hivemind/.venv/lib/python3.11/site-packages/conductor/client/workflow/conductor_workflow.py", line 267, in to_workflow_def
tasks=self.__get_workflow_task_list(),
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/discord/github.com/discord/discord/discord_hivemind/.venv/lib/python3.11/site-packages/conductor/client/workflow/conductor_workflow.py", line 289, in __get_workflow_task_list
converted_task = task.to_workflow_task()
^^^^^^^^^^^^^^^^^^^^^^^
File "/home/discord/github.com/discord/discord/discord_hivemind/.venv/lib/python3.11/site-packages/conductor/client/workflow/task/task.py", line 140, in to_workflow_task
if self._cache_ttl_second > 0 and self._cache_key is not None:
^^^^^^^^^^^^^^^^^^^^^^
File "/home/discord/github.com/discord/discord/discord_hivemind/.venv/lib/python3.11/site-packages/conductor/client/workflow/task/task.py", line 185, in __getattribute__
raise ae
File "/home/discord/github.com/discord/discord/discord_hivemind/.venv/lib/python3.11/site-packages/conductor/client/workflow/task/task.py", line 180, in __getattribute__
val = super().__getattribute__(__name)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AttributeError: 'SimpleTask' object has no attribute '_cache_ttl_second'. Did you mean: 'cache_ttl_second'?
```

Reproduce the failure with the README files greetings_worker.py, greetings_workflow.py, and helloworld.py using uv run helloworld.py. Start with the task and workflow code named in the traceback, especially task.py and conductor_workflow.py, and verify that the example registers and runs without the reported AttributeError.

由索引模型根据 Issue 内容生成。