add parameter set_batch_size_to_split_size to DatasetDict.map

[ArneBinder]

from the docstring:

set_batch_size_to_split_size: If enabled, set the batch_size to the size of the respective split
    when calling map() on it. This is useful to transform whole splits when using it in
    combination with batched=True.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.35%. Comparing base (ef8f2d7) to head (8690c7b).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #155      +/-   ##
==========================================
+ Coverage   92.34%   92.35%   +0.01%     
==========================================
  Files          10       10              
  Lines         901      903       +2     
==========================================
+ Hits          832      834       +2     
  Misses         69       69              

Flag	Coverage Δ
	92.35% <100.00%> (+0.01%)	⬆️

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