Speed up cloned geography assignment

[MaxGhenis]

Summary

• replace per-clone object-string collision scans with a per-record CD-code lookup table
• resample only records that still collide instead of drawing replacements for every record
• add a changelog entry

Tests

• uv run pytest tests/unit/calibration/test_clone_and_assign.py -q
• uv run ruff check policyengine_us_data/calibration/clone_and_assign.py tests/unit/calibration/test_clone_and_assign.py
• git diff --check

Local benchmark: a 11,999-household x 430-clone mocked assignment completed in 1.8s.