Use 2024 SOI filing-season EITC totals

[MaxGhenis]

Summary

• add the new Ledger 2024 SOI filing-season EITC total alias to the US hard-target source surface
• make cross-period EITC uprating choose the latest source-backed total deterministically instead of relying on registry order
• record the source period and Ledger source record that provide each EITC uprating index
• update release critical-fit gates to validate the 2024 filing-season EITC total amount and return-count diagnostics
• cover amount and return-count factors in tests

Depends on PolicyEngine/arch-data#58.

EITC uprating factors

• amount: 2024 filing-season total / 2023 decomposition total = 1.04182360105362 in the real Ledger fact integration check
• return count: 23,837,149 / 24,439,936 = 0.975335982876551

Validation

• uv run --with ruff ruff format tools/build_us_fiscal_refresh_release.py packages/populace-build/tests/test_us_fiscal_refresh_builder.py packages/populace-build/src/populace/build/us/fiscal_targets.py packages/populace-build/src/populace/build/us/source_coverage.py packages/populace-build/tests/test_us_fiscal_targets.py packages/populace-build/tests/test_us_source_coverage.py --check
• uv run --with ruff ruff check tools/build_us_fiscal_refresh_release.py packages/populace-build/tests/test_us_fiscal_refresh_builder.py packages/populace-build/src/populace/build/us/fiscal_targets.py packages/populace-build/src/populace/build/us/source_coverage.py packages/populace-build/tests/test_us_fiscal_targets.py packages/populace-build/tests/test_us_source_coverage.py
• uv run python -m pytest packages/populace-build/tests/test_us_fiscal_targets.py packages/populace-build/tests/test_us_source_coverage.py packages/populace-build/tests/test_us_fiscal_refresh_builder.py -q
• Real integration check with Ledger PR facts: EITC amount decomposition targets sum to .041649B and return-count targets sum to 23,837,149, with metadata pointing to the filing-season source records.