Fix response parsing for MultipleItems requests

[Saltiola7]

Issue Description

When using the MultipleItems class to create multiple items at once, the SDK incorrectly tried to parse the API response as a CollectionItem object. However, when creating multiple items, the API returns a response with an items field containing a list of items, which should be parsed as a CollectionItemList object.

This caused a validation error:

pydantic_core._pydantic_core.ValidationError: 1 validation error for CollectionItem
field_data
  Field required [type=missing, input_value={'items': [{'id': '...', ...}]}, input_type=dict]

Solution

I modified the create_item method in client.py to check if the request is a MultipleItems object and, if so, parse the response as a CollectionItemList instead of a CollectionItem. This correctly handles the different response formats based on the request type.

Changes:

1. Updated the return type annotation to typing.Union[CollectionItem, CollectionItemList]
2. Added a conditional check to use the appropriate model for parsing based on the request type

Testing

I've tested this change by creating multiple items at once using the MultipleItems class, and the SDK now correctly parses the response without validation errors.

[zplata]

Hi @Saltiola7 - we'll take a look at this. Which version of the lib are you using?

[Saltiola7]

2.0.0b1 in the pyproject.toml