chore(ci): implement unit test for data_extractor

[soonum]

This is the first batch of unit tests. More cases will follow to improve coverage along with integration tests to test file generation.

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This change is 

[IceTDrinker]

are the tests run in CI somehow ?

@IceTDrinker reviewed 4 of 4 files at r1, all commit messages.
Reviewable status: all files reviewed, 2 unresolved discussions (waiting on @soonum)

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ci/data_extractor/tests/test_unit.py line 351 at r1 (raw file):

if __name__ == "__main__":
    unittest.main()

unclear to me whether things are actually tested

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ci/data_extractor/tests/__init__.py line 5 at r1 (raw file):

# Add data_extractor sources to the Python path.
path = os.path.abspath(os.path.join(os.path.dirname(__file__), "../src"))

this is yuck, isn't there a way to properly load a python module ?

if you need to setup a project with uv (written in rust so should be ok to install) or something please do that