[CHORE] Remove NLP features

[joweich]

NLP features were introduced to chat-miner around 2 years ago (b1daa4e). Since then, the field of natural language has grown significantly, with many options presenting valid approaches to extract text sentiment, e.g. LLMs.
To keep the library lean, chat-miner won't ship NLP features from v0.6.0 on.
Our dataframe-based representation of chat data may be consumed directly by any custom logic for sentiment extraction.

[codecov-commenter]

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.11%. Comparing base (796bb3e) to head (39bf62f).
Report is 1 commits behind head on main.

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Additional details and impacted files

@@           Coverage Diff           @@
##             main     #154   +/-   ##
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  Coverage   90.11%   90.11%           
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  Files           1        1           
  Lines         263      263           
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  Hits          237      237           
  Misses         26       26           

Flag	Coverage Δ
unittests	90.11% <ø> (ø)

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