Move disability benefit reported amount mapping to UK data

[MaxGhenis]

Summary

• Make PIP, DLA, and Attendance Allowance category variables direct model input leaves.
• Remove pip_*_reported, dla_*_reported, and attendance_allowance_reported from the model and uprating docs.
• Add tests that disability benefit categories default or can be set directly, and reported amount variables are no longer model inputs.

Tests

• uv run ruff check policyengine_uk/variables/input/dla_sc_category.py policyengine_uk/variables/input/dla_m_category.py policyengine_uk/variables/input/pip_dl_category.py policyengine_uk/variables/input/pip_m_category.py policyengine_uk/variables/gov/dwp/aa_category.py policyengine_uk/tests/test_deterministic_variables.py
• uv run pytest -q policyengine_uk/tests/code_health policyengine_uk/tests/test_deterministic_variables.py

[MaxGhenis]

Opened the uk-data companion: PolicyEngine/policyengine-uk-data#383.

It maps reported PIP/DLA/Attendance Allowance amounts to category inputs in the data pipeline, keeps reported amounts only as internal FRS/imputation intermediates, strips them before saved datasets, and updates the public transfer dataset to emit PIP categories directly.