Fix data hyper-cleaning pytest script path

[alceops]

Fixes #32.

Summary

• Replace the hard-coded GitHub Actions workspace path in the data hyper-cleaning pytest wrapper with a path derived from Path(__file__).
• Use sys.executable so the example test runs with the same Python interpreter/virtualenv that invoked pytest.
• Keep the existing parametrized coverage and CLI arguments unchanged.

Verification

• python3 -m py_compile examples/data_hyper_cleaning/test_data_hyper_cleaning.py
• git diff --check
• Static assertion that /home/runner/work/BOAT is no longer present in the test file and the script path is repo-relative
• /tmp/boat-venv/bin/python -m pytest examples/data_hyper_cleaning/test_data_hyper_cleaning.py --collect-only -q (68 tests collected)

Not fully run locally: executing the example currently needs the project ML dependencies; in this minimal verification venv, the first selected test stops at the pre-existing missing torch import. This PR only changes the test wrapper path/interpreter selection.

No private data, paid compute, GPU, secrets, deploy, account setup, or production access used.