Utah CTC contrib reform changes years in which its in_effect switch is off #9842

Switching on gov.contrib.states.ut.ctc.in_effect from 2026 changes Utah income tax in 2024 and 2025, when the switch is still false.

Repro

Run on the head of #9628 (743b6dfd3d, which is main at ea79c39fb7 plus that PR), with policyengine-core 3.32.15:

from policyengine_us import Simulation

YEARS = (2024, 2025, 2026)
members = ["adult1", "adult2", "child1", "child2"]
situation = {
    "people": {
        "adult1": {
            "age": {y: 35 for y in YEARS},
            "employment_income": {y: 110_000 for y in YEARS},
        },
        "adult2": {"age": {y: 35 for y in YEARS}},
        "child1": {"age": {y: y - 2023 for y in YEARS}},
        "child2": {"age": {y: y - 2022 for y in YEARS}},
    },
    "tax_units": {"tu": {"members": members}},
    "marital_units": {"mu": {"members": ["adult1", "adult2"]}},
    "households": {
        "hh": {"members": members, "state_code": {y: "UT" for y in YEARS}}
    },
}
baseline = Simulation(situation=situation)
reformed = Simulation(
    situation=situation,
    reform={"gov.contrib.states.ut.ctc.in_effect": {"2026-01-01.2100-12-31": True}},
)
for y in YEARS:
    print(
        y,
        reformed.calculate("household_net_income", y)[0]
        - baseline.calculate("household_net_income", y)[0],
    )

Cause

create_ut_ctc_reform (policyengine_us/reforms/states/ut/ctc/ut_ctc_reform.py) installs the reform for the whole simulation when in_effect is true in any of the five years from the simulation's start. The variables it installs (ut_ctc_eligible_children, ut_ctc_potential and ut_refundable_ctc) replace the baseline ones, and none of them reads in_effect, so they run in every year, including the years before the switch turns on.

Other contrib reforms that pair look-ahead detection with formulas that don't read the switch would behave the same way. I have only checked this one.

Found while reviewing #9628. On main, that PR's example (which also changes the reform amounts from 2026) shows a larger 2024–2025 change, because the changed amounts also leak back to 2015. #9628 fixes the leak but not this.