Widen disability benefit flags from reported amounts

[MaxGhenis]

Summary

• widen is_disabled_for_benefits to include AA, SDA, incapacity benefit, IIDB, AFCS, and ESA reported amounts
• treat Attendance Allowance as a severe-disability signal, and higher-rate AA as an enhanced-disability signal
• update focused disability-benefit tests for the wider base flag and AA-derived stronger flags

Closes #400

Tests

• uv run --python 3.13 --frozen ruff format --check policyengine_uk_data/datasets/disability_benefits.py policyengine_uk_data/tests/test_disability_benefits.py
• uv run --python 3.13 --frozen ruff check policyengine_uk_data/datasets/disability_benefits.py policyengine_uk_data/tests/test_disability_benefits.py
• uv run --python 3.13 --frozen pytest policyengine_uk_data/tests/test_disability_benefits.py policyengine_uk_data/tests/test_frs_only_imputation.py::test_frs_only_recomputes_disability_flags_after_amount_imputation -q
• git diff --check