take docstrings outside imputer base class

[solegalli]

No description provided.

[codecov]

Codecov Report

Merging #605 (5a2f8cb) into main (a1da8c2) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #605   +/-   ##
=======================================
  Coverage   97.80%   97.80%           
=======================================
  Files          92       92           
  Lines        3510     3511    +1     
  Branches      684      684           
=======================================
+ Hits         3433     3434    +1     
  Misses         29       29           
  Partials       48       48           

Impacted Files	Coverage Δ
feature_engine/imputation/arbitrary_number.py	100.00% <ø> (ø)
feature_engine/_docstrings/fit_attributes.py	100.00% <100.00%> (ø)
feature_engine/_docstrings/methods.py	100.00% <100.00%> (ø)
feature_engine/imputation/base_imputer.py	100.00% <100.00%> (ø)
feature_engine/imputation/categorical.py	95.23% <100.00%> (ø)
feature_engine/imputation/end_tail.py	92.68% <100.00%> (+0.18%)	⬆️
feature_engine/imputation/mean_median.py	96.15% <100.00%> (+0.15%)	⬆️
feature_engine/imputation/random_sample.py	95.58% <100.00%> (ø)

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