Add a test split loader for Drugprot

[RainbowRivey]

Original HF loader skips test split, to be fixed here

TODOs:

• [x] add a copy of the bigbio HF script to this repo
• [x] add tests for that
• [x] adjust the HF script to also create a test split (also adjust tests)
• [x] adjust the PIE script to use the local HF script (also adjust tests)
• [x] create a PR at the bigbio HF script with these changes
• [x] when the HF bigbio is updated (https://github.com/bigscience-workshop/biomedical/pull/928 is merged and it is also updated on huggingface.co), update the revision of the PIE script
• [x] merge this PR

IMPORTANT: We do not want to execute pre-commit on this because we want to keep the changes as less as possible because this should be re-integrated into to https://huggingface.co/datasets/bigbio/drugprot.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 96.82%. Comparing base (ae49e5d) to head (0212c27). Report is 1 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #142 +/- ## ========================================== - Coverage 98.27% 96.82% -1.46% ========================================== Files 1 1 Lines 58 63 +5 ========================================== + Hits 57 61 +4 - Misses 1 2 +1 ```

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