Defined Benefits pension system not handling parameters object sizes correctly

[jdebacker]

The defined benefits system functions have not been updated for at least two time varying parameters: earnings ability and retirement age. Time varying earnings ability was added in PR #895. Time varying retirement age was added in PR #433.

The pensions.py functions used for computing defined benefits pension amounts should be updated and tested to work with these new dimensions.

The bug here also suggests new tests: SS and TPI tests should include model runs with each pension system.

[marcelolafleur]

PR #1167 fixes the crash-level problems in the DB and PS systems (array/scalar mismatches with a real Specifications object) and makes the DB system solve the steady state and the transition path. Mapping what remains open here after that PR:

• Time-varying retirement age in the DB/NDC/PS formulas — the PR uses the steady-state value throughout.
• Time-varying earnings profiles in the same formulas — the PR uses the steady-state profile.
• Pre-time-path histories: the PR anchors pre-period-0 wages to the period-0 wage of the current path and takes labor from the model's initial condition. A fully history-consistent treatment (each cohort's own solved pre-path labor) is still open.
• TPI-level model-run tests for each pension system (the PR adds a steady-state solve test for DB).

Downstream context: OG-BRA now runs the DB system for Brazil's RGPS, so these have a live user.