Fixes #8656

Problem

The bundled Ohio refundable-EITC contrib reform (gov.contrib.states.oh.child_poverty_impact_dashboard.eitc.in_effect) ran without crashing but was functionally wrong on two fronts — same shape as the MO and UT bugs fixed in #8642 and #8645, but no add() string crash:

1. Zero refund at zero liability. oh_refundable_eitc.formula returned tax_unit("oh_eitc", period) — the applied nonrefundable-capped EITC. A zero-liability filer's oh_eitc is 0, so the reform's oh_refundable_eitc was also 0 — no refund paid in exactly the case refundability is meant to address.

2. Other Ohio non-refundable credits discarded. oh_non_refundable_credits.formula returned just tax_unit("oh_non_refundable_eitc", period) (= 0 under the reform), silently zeroing out every other non-refundable credit walked by the baseline ordered list (oh_cdcc, oh_senior_citizen_credit, oh_retirement_credit, oh_non_public_school_credits, oh_exemption_credit, oh_joint_filing_credit, plus oh_adoption_credit for pre-2023 years). An OH filer claiming any of those lost them all whenever the reform was active.

Fixes in oh_refundable_eitc_reform.py

oh_refundable_eitc now reads oh_eitc_potential (uncapped at liability; OH does not apply a separate cap layer above the potential, so this is the full refundable amount). Mirrors the MO mo_wftc → mo_wftc_potential change in #8642 and the UT ut_eitc → ut_eitc_potential change in #8645.

oh_non_refundable_credits now walks the same ordered list the baseline uses (gov.states.oh.tax.income.credits.non_refundable) via ordered_capped_state_non_refundable_credits, with oh_eitc filtered out of the list since the reform pays it as refundable. Identical pattern to the UT fix.

Verification

• All four updated contrib tests pass (drive from federal eitc and oh_income_tax_before_non_refundable_credits rather than injecting capped oh_eitc, in line with the new uncapped behaviour).
• New tests/policy/reform/oh_refundable_eitc.yaml adds four regression tests: full refundable payout at zero liability (asserting oh_income_tax goes negative, i.e. the refund is actually paid); confirmation that oh_joint_filing_credit still applies under the reform (proves the other credits are no longer discarded); no double-counting when liability partially absorbs other credits; and the filtered ordered walk capping multiple non-EITC credits at remaining liability.
• All 234 Ohio baseline tests still pass.
• The test_non_refundable_credit_downstream_consumers.py invariant still passes (the reform's reference to oh_eitc in the filter is unchanged).

Why this slipped through

Same test-shielding pattern as MO/UT — see the OH stanza of the bug-pattern analysis in the parent issue. The existing contrib tests pinned oh_eitc: 500 as input and only checked oh_refundable_eitc / oh_non_refundable_eitc / oh_non_refundable_credits with no other OH credits present, which dodged both broken code paths.

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