Four more variables declare uprating but are missing from uprating_indices.yaml

Follow-up to #1859 / #1860, raised in review of that PR. Same root cause, different variables — filed separately to keep the fix there focused.

Root cause, stated for the record

The class-level uprating = "..." attribute on a Variable is dead metadata in this repo: nothing reads it, and policyengine-core only inspects it to refuse combining it with its own @uprated decorator. data/uprating_indices.yaml is the only mechanism that actually applies uprating (apply_single_year_uprating / reset_growthfactor_uprating in data/economic_assumptions.py).

So a variable can declare an index and silently never be uprated. That is what #1859 observed for electricity_consumption and gas_consumption.

Four more affected

Measured on enhanced_frs_2024_25, household means, 2024 → 2027, all flat:

Separately, savings_interest_income declares indices.ons.household_interest_income, but the YAML applies per_capita.gdp to it — a mismatch rather than an omission.

Two of the four point at indices that may have no yoy_growth parameter yet, so fixing them is likely more than a YAML addition.

Suggested durable fix

A code-health test (natural home policyengine_uk/tests/code_health/) asserting that every variable declaring uprating appears in uprating_indices.yaml under the matching index. That makes the gap visible instead of silent, and would have caught #1859 at the point it was introduced.

Credit to @juaristi22, who found these while reviewing #1860.

Start with data/uprating_indices.yaml and the variable declarations, then read apply_single_year_uprating and reset_growthfactor_uprating in data/economic_assumptions.py. Review policyengine_uk/tests/code_health/ for the proposed consistency check; done means the four declarations are accounted for with matching uprating configuration, including any required growth parameters.