Add `inherit_docstring` decorator to inherit docstring

[haiiliin]

Closes #9.

[AntoineD]

Hello and thank you for this PR!

Like for the metaclasses, would you mind creating one decorator per style?

For performance reasons, would you also mind preventing the decorator from changing the docstring after the first call?

[codecov-commenter]

Codecov Report

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

Project coverage is 100.00%. Comparing base (be17920) to head (daddf96). Report is 46 commits behind head on main.

Additional details and impacted files

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  Coverage   100.00%   100.00%           
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  Files            6         6           
  Lines          273       281    +8     
  Branches        61        61           
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+ Hits           273       281    +8     

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