Align SPM thresholds and clone priors

[MaxGhenis]

Revives the safe parts of #702 after rebasing on latest main.

Changes:

• replace spm-calculator base thresholds with published Census SPM reference thresholds through 2024, with CPI-U fallback for future years
• make congressional-district geoadj tenure-specific and pass tenure-aware geoadj through extended CPS, local-area, and chunked clone SPM threshold recalculation
• preserve positive household weights exactly while keeping zero-weight clone priors at tiny epsilon before sparse reweighting

Intentionally left out:

• the old Align SPM thresholds and stabilize clone-half priors #702 NYC/CD local-area changes, because review flagged that as a regression from block-based geography
• survey SPM direct-sum target additions, because current main explicitly drops those target concepts

Tests:

• .venv/bin/python -m pytest -q tests/unit/calibration/test_spm_thresholds.py tests/unit/test_extended_cps.py tests/unit/test_enhanced_cps_clone_diagnostics.py tests/unit/calibration/test_entity_clone.py tests/integration/test_chunked_matrix_builder.py tests/unit/test_etl_national_targets.py tests/unit/calibration/test_loss_targets.py tests/unit/test_small_enhanced_cps.py
• .venv/bin/ruff check policyengine_us_data/utils/spm.py policyengine_us_data/calibration/calibration_utils.py policyengine_us_data/calibration/entity_clone.py policyengine_us_data/calibration/publish_local_area.py policyengine_us_data/datasets/cps/enhanced_cps.py policyengine_us_data/datasets/cps/extended_cps.py tests/unit/calibration/test_spm_thresholds.py tests/unit/test_extended_cps.py tests/unit/test_enhanced_cps_clone_diagnostics.py
• .venv/bin/ruff format --check policyengine_us_data/utils/spm.py policyengine_us_data/calibration/calibration_utils.py policyengine_us_data/calibration/entity_clone.py policyengine_us_data/calibration/publish_local_area.py policyengine_us_data/datasets/cps/enhanced_cps.py policyengine_us_data/datasets/cps/extended_cps.py tests/unit/calibration/test_spm_thresholds.py tests/unit/test_extended_cps.py tests/unit/test_enhanced_cps_clone_diagnostics.py