Type hints incomplete for objects

### Description of the Issue
Type hints are present for methods, but type hints for objects (e.g. File) are missing the attributes. Running a tool like mypy or intellij with type hinting complains about attributes:
"Item" has no attribute "content_created_at" [attr-defined]

### Steps to Reproduce
pip install mypy
mypy test/unit/object/test_folder.py

or open test_folder.py in Intellij

### Error Message, Including Stack Trace
get errors like on line 286 assert new_file.description == file_description # File has no attribute 'description'

### Versions Used
Python SDK: 3.0.1, python 3.8.8