Add Chemprot dataset

[kai-car]

Created loading script chemprot.py for ChemProt dataset available on Hugging Face bigbio/chemprot and associated test script test_chemprot.py. Currently all tests run successfully. However, still working on completion.
(Note: The first pull request #137 was closed due to rebasing the branch)

Finally, this will include:

• requirements.txt
• test HF dataset
• document type
• HF example <-> document
• test HF example <-> document
• test PIE dataset
• document converts
• test document converters
• README.md

[codecov]

Codecov Report

Attention: Patch coverage is 92.23301% with 8 lines in your changes missing coverage. Please review.

Project coverage is 92.23%. Comparing base (38b9580) to head (c251c02).
Report is 2 commits behind head on main.

Files	Patch %	Lines
dataset_builders/pie/chemprot/chemprot.py	92.23%	8 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #138      +/-   ##
==========================================
+ Coverage   91.40%   92.23%   +0.83%     
==========================================
  Files          10        1       -9     
  Lines         814      103     -711     
==========================================
- Hits          744       95     -649     
+ Misses         70        8      -62     

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[kai-car]

From my perspective general functionality of chemprot.py implemented. Although some minor changes might still be needed.

[ArneBinder]

Thanks! Just some minors.