fix: return DatasetDefinition copy by DatasetLibrary.get()

[dkrako]

Description

#914 exposed a bug in resample(): the experiment of the dataset definition is not just updated in the GazeDataFrame itself, but also in the DatasetLibrary. This really shouldn't happen.

See the corresponding discussion.

#914 will be merged with the adjusted docstring, but this PR needs to revert the change to the docstring again.

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Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change is or requires a documentation update

How Has This Been Tested?

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (87487d0) to head (9d101b9).

Additional details and impacted files

@@            Coverage Diff            @@
##              main     #1023   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files           79        79           
  Lines         3588      3586    -2     
  Branches       645       645           
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- Hits          3588      3586    -2     

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[dkrako]

I just don't get it...

How can test_returned_definition_is_copy fail if I clearly use deepcopy() in DatasetLibrary.get()?

[dkrako]

Ah now I think I know why this happened. The returned definition was the class not an instance. #914 has changed this accordingly which is good. The same class is always the same, regardless of using deepcopy.

Hope the tests will pas now.