type checker fixes

[jangevaare]

This pull request incorporates quick fixes from running the latest version of ty against the codebase for typing issues.

• Removed unnecessary type: ignore comments in loops over clients and DataFrame rows, improving type safety in build_client_lookup and build_preprocess_result (pipeline/bundle_pdfs.py, pipeline/preprocess.py). [1] [2]
• Added @overload type annotations and improved type handling for the filter_columns utility, allowing it to handle both None and pd.DataFrame inputs more robustly (pipeline/preprocess.py).
• Added missing imports (e.g., overload from typing) and made minor code style improvements, such as whitespace and line breaks, for better readability (pipeline/preprocess.py). [1] [2] [3] [4] [5]
• Updated unit tests to use pd.Index for DataFrame columns and improved test assertions for clarity and correctness (tests/unit/test_preprocess.py). [1] [2]

[codecov]

Codecov Report

❌ Patch coverage is 87.50000% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
pipeline/preprocess.py	85.71%	0 Missing and 1 partial ⚠️

📢 Thoughts on this report? Let us know!