AL, KY, MS, ND and OH dashboard EITC contrib reforms raise 'mixes computation modes' when switched on #9843

Switching on the child poverty impact dashboard EITC reform for Alabama, Kentucky, Mississippi, North Dakota or Ohio makes the simulation raise:

ValueError: Variable "al_refundable_credits" mixes computation modes: formula and uprating. Variables must use at most one of formula, adds/subtracts, or uprating; plain input or constant variables should use none.

The other four states raise the same error for ky_refundable_credits, ms_refundable_credits, nd_refundable_credits and oh_refundable_credits.

Repro

Run on the head of #9628 (743b6dfd3d, which is main at ea79c39fb7 plus that PR), with policyengine-core 3.32.15. Each state raises while building the simulation or computing household net income:

from policyengine_us import Simulation

for state in ("al", "ky", "ms", "nd", "oh"):
    switch = f"gov.contrib.states.{state}.child_poverty_impact_dashboard.eitc.in_effect"
    sim = Simulation(
        situation={
            "people": {
                "parent": {"age": 30, "employment_income": 15_000},
                "child": {"age": 5},
            },
            "tax_units": {"tu": {"members": ["parent", "child"]}},
            "households": {
                "hh": {"members": ["parent", "child"], "state_code": state.upper()}
            },
        },
        reform={switch: {"2026-01-01.2100-12-31": True}},
    )
    sim.calculate("household_net_income", 2026)

#8640 (Missouri) and #8644 (Utah) reported the dashboard EITC reforms for two other states crashing when triggered, and both are closed. These five are still open. Found while reviewing #9628, which does not change this.