Add SSA supplement source package

[MaxGhenis]

Summary

• add a compact SSA Annual Statistical Supplement 2025 source package for 2024 OASDI and SSI payment totals
• include the packaged source manifest/CSV and source-package alias
• cover explicit SSA bundle output and fixture-count validation

Verification

• uv run ruff check arch db tests/test_arch_bundle.py tests/test_arch_source_package.py
• uv run pytest tests/test_arch_bundle.py tests/test_arch_source_package.py tests/test_arch_suite.py -q
• uv run pytest -q
• uv build --wheel --out-dir /tmp/arch-ssa-dist, with SSA package/data files present in the wheel