Adding a grid_scan plan to the queueserver fails pydantic validation

[Cathyhjj]

Describe the bug
When adding grid scan on firefly ui, it didn't add to the queueserver

Error message

Grid plan failed to be added to queue server

For further information visit https://errors.pydantic.dev/2.9/u/schema-for-unknown-type
Plan: {'item_type': 'plan',
 'name': 'rel_grid_scan',
 'args': [['It'], 'Sam H Cds', -10.0, 10.0, 1, 'Sam H Cds', -10.0, 10.0, 1],
 'kwargs': {'snake_axes': False, 'md': {}}}
Traceback (most recent call last):
  File "/home/beams0/S25IDCUSER/miniforge3/envs/haven/lib/python3.10/site-packages/qasync/__init__.py", line 780, in _error_handler
    task.result()
  File "/home/beams0/S25IDCUSER/miniforge3/envs/haven/lib/python3.10/site-packages/firefly/controller.py", line 660, in add_queue_item
    await self._queue_client.add_queue_item(item)
bluesky_queueserver_api.comm_base.RequestFailedError: Request failed: Failed to add an item: Plan validation failed: Unable to generate pydantic-core schema for <class 'collections.abc.Iterable'>. Set `arbitrary_types_allowed=True` in the model_config to ignore this error or implement `__get_pydantic_core_schema__` on your type to fully support it.

If you got this error by calling handler(<some type>) within `__get_pydantic_core_schema__` then you likely need to call `handler.generate_schema(<some type>)` since we do not call `__get_pydantic_core_schema__` on `<some type>` otherwise to avoid infinite recursion.