docs: fix import statements in cognite/client/_api/assets.py

[miladh]

Also avoid abbreviations

Description

Please describe the change you have made.

Checklist:

• [ ] Tests added/updated.
• [ ] Documentation updated. Documentation is generated from docstrings - these must be updated according to your change. If a new method has been added it should be referenced in cognite.rst in order to generate docs based on its docstring.
• [ ] Changelog updated in CHANGELOG.md.
• [ ] Version bumped. If triggering a new release is desired, bump the version number in _version.py and pyproject.toml per semantic versioning.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

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Additional details and impacted files

@@            Coverage Diff            @@
##             master    #1749   +/-   ##
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  Coverage          ?   92.52%           
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  Files             ?      124           
  Lines             ?    18444           
  Branches          ?        0           
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  Hits              ?    17065           
  Misses            ?     1379           
  Partials          ?        0           

Files	Coverage Δ
cognite/client/_api/assets.py	97.71% <ø> (ø)
cognite/client/_api/extractionpipelines.py	97.70% <ø> (ø)