- Add PL 94-171 parser for legacy pipe-delimited format
- Download bulk zip files from Census FTP instead of API calls
- Fix DuckDB query to use GEO_ID column name from parquet
- Update test mocks to serve zip files instead of JSON responses
- Bump version to 0.1.5

This eliminates timeout issues with the Census API for large states
like California by downloading the pre-built redistricting files.

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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>