fix(exceptions): rename InvalidDatasetError.format to data_format

[himanshu231204]

Summary

Resolves #70. InvalidDatasetError declared a constructor parameter named format, which shadows Python's built-in format(). This is a code-quality/footgun issue flagged by linters and confuses readers who expect format to be the builtin.

The parameter (and its self.format attribute) is renamed to data_format across the exception definition and every call site. The details dict key remains "format" since it is only a string payload key, not a Python identifier, so there is no shadowing concern and no change to the serialized error output.

Changes

• openagent_eval/exceptions/dataset.py — rename format param/attribute/docstring to data_format.
• openagent_eval/datasets/factory.py — update data_format=config.format kwarg.
• openagent_eval/datasets/json_loader.py, jsonl_loader.py, csv_loader.py, hf_loader.py, pdf_loader.py — update data_format= kwargs at all raise sites.
• tests/unit/test_exceptions.py — update the InvalidDatasetError test to use data_format=.

Testing

• pytest tests/unit/test_exceptions.py — 26 passed.
• pytest tests/unit/test_datasets — 83 passed. (The 4 test_pdf_loader failures are pre-existing and environmental: pypdf is not installed in this environment. The error output confirms the new kwarg is passed correctly: InvalidDatasetError: ... (format=pdf, ...).)
• ruff check openagent_eval/exceptions/dataset.py — all checks passed. Remaining ruff warnings in datasets/ are pre-existing and unrelated to this change.

Checklist

• Branch created off main (fix/70-...)
• InvalidDatasetError no longer shadows the format built-in
• All call sites updated
• Tests updated and passing
• Lint clean on changed exception module

[github-actions]

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