Offer household years separately from society-wide years in the country metadata #4160

Why

The /{country}/metadata response has one year list, economy_options.time_period, and the app reads it for every year menu: household reports, society-wide reports and the policy editors.

The plan is for the Public API to refuse society-wide (population-wide) US runs for 2022 and 2023, because the data for those years is nearly empty, while still allowing household calculations for those years. With a single year list, narrowing the society-wide years would also remove 2022 and 2023 from household reports. Household years and society-wide years therefore need separate lists in the metadata.

What #4159 adds

#4159 adds household_options.time_period to the /{country}/metadata response, with items in the same shape as economy_options.time_period items ({"name": <int year>, "label": "<year>"}). It leaves economy_options unchanged.

• US: the years the bundle's certified SPM forecast covers, up to the last year in the CPI-U parameter's source file (gov.bls.cpi.cpi_u), newest first. With the current bundle this is 2035 to 2022. Without a certified SPM forecast, the US household years are the US society-wide years.
• UK: the rule for the UK society-wide years (uk_economy_years), currently 2024 to 2032.
• Any other country: its society-wide years.

Building the list loads no dataset and runs no simulation, so it adds no meaningful startup time.

Later

PolicyEngine/policyengine-app-v2#1515 makes the app read household_options.time_period for household year menus and the policy editors, and economy_options.time_period for society-wide ones. After that is deployed, a later Public API PR will narrow the US economy_options.time_period to start at 2024 and refuse society-wide requests for years outside it.