fix DataFrame.applymap has been deprecated.

[mdclone-oa]

fix issue #258

/usr/local/lib/python3.12/site-packages/pandarallel/data_types/dataframe.py:69: FutureWarning: DataFrame.applymap has been deprecated. Use DataFrame.map instead.
return data.applymap(user_defined_function)

change applymap to map and tests

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (46fc0e5) 91.37% compared to head (861d0d8) 86.37%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #259      +/-   ##
==========================================
- Coverage   91.37%   86.37%   -5.00%     
==========================================
  Files          12       12              
  Lines         580      580              
==========================================
- Hits          530      501      -29     
- Misses         50       79      +29     

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[shermansiu]

Unless we're dropping support for Pandas versions < 2.1, I'm against this, especially since Pandas 2.1 was released relatively recently.

There's also no reason to change the minimum Python version to 3.9...