Add census block-level geographic assignment with comprehensive lookups (#484)

* Add census block-level geographic assignment with comprehensive lookups

- Assign census blocks using P(block|CD) from Census population data
- Look up all geography from block GEOID for consistency:
  - County, tract, state (from GEOID structure)
  - CBSA/metro area (via NBER county crosswalk)
  - SLDU/SLDL (state legislative districts)
  - Place/City FIPS (via Census BAF)
  - PUMA (via tract crosswalk)
  - VTD (voting tabulation district)
- Add block_crosswalk.csv.gz (8.1M blocks) with BAF data
- Add make_block_crosswalk.py to generate crosswalk from Census BAFs
- Add comprehensive tests for all geography lookups

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

* Add changelog entry

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

* Fix black formatting

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

* Trigger CI

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

* Fix black formatting (26.1.0)

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

* Save all geography variables to CD-stacked datasets

Updates stacked_dataset_builder.py to:
- Set all geography variables from block assignment (block_geoid, tract_geoid,
  cbsa_code, sldu, sldl, place_fips, vtd, puma)
- Include these variables in the saved h5 files

These variables enable granular geographic analysis at multiple levels:
state legislative districts, census tracts, metro areas, cities, etc.

Requires policyengine-us#7249 for the variable definitions.

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

* Add ZCTA (ZIP code) lookup from census block

- Add ZCTA column to block_crosswalk.csv.gz from Census relationship file
- Add get_zcta_from_block() function and include zcta in assign_geography_for_cd()
- Save zcta to CD-stacked dataset output
- Add tests for ZCTA lookup

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

* Update policyengine-us to v1.524.1 for geography variables

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

---------

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>
Co-authored-by: baogorek@gmail.com <baogorek@gmail.com>

Author: 3 people

changelog_entry.yaml

@@ -0,0 +1,8 @@
+- bump: minor
+  changes:
+    added:
+    - Census block-level geographic assignment for households in CD-stacked datasets
+    - Comprehensive geography variables in output (block_geoid, tract_geoid, cbsa_code, sldu, sldl, place_fips, vtd, puma, zcta)
+    - Block crosswalk file mapping 8.1M blocks to all Census geographies
+    - Block-to-CD distribution file for population-weighted assignment
+    - ZCTA (ZIP Code Tabulation Area) lookup from census block