Variable to amend: tx_chip_premium, mi_chip_premium, la_chip_premium

tx_chip_premium, mi_chip_premium and la_chip_premium charge the tax unit whenever any member has is_chip_eligible:

has_chip_member = add(tax_unit, period, ["is_chip_eligible"]) > 0

is_chip_eligible is true for every CHIP category, including PREGNANT_FCEP. Texas (207% FPL), Michigan (200%) and Louisiana (214%) all have a from-conception-to-end-of-pregnancy (FCEP) income limit in parameters/gov/hhs/chip/fcep/income_limit.yaml. So a tax unit whose only CHIP-eligible member is a pregnant person covered through FCEP can be charged the children's CHIP premium or enrollment fee.

#10363 fixed the same pattern for Missouri. mo_chip_premium now triggers on is_chip_eligible_child, because Missouri charges no premium for pregnant women or unborn children (CHIP SPA MO-15-0009; RSMo 208.640.1). AL, CT, GA, IA, ID, IL, IN, MA, NY and WI already trigger on is_chip_eligible_child.

To check before changing

Whether each state charges its CHIP premium or enrollment fee for unborn-child (FCEP) coverage:

• Texas: CHIP perinatal coverage vs. the CHIP enrollment fee (Texas Works Handbook D-1820, the reference tx_chip_premium cites).
• Michigan: MIChild premium and the FCEP population.
• Louisiana: LaCHIP Affordable Plan premium vs. LaMOMS/CHIP unborn option coverage.

Federal law bars cost sharing for pregnancy-related assistance (42 USC 1397cc(e)(2)) but lists premiums separately, so each state's own plan or rule decides. Not checked yet.

Suggested fix

Where the state's rules confirm that pregnancy-only (FCEP) coverage carries no premium, trigger the premium on is_chip_eligible_child, as mo_chip_premium now does. Add a YAML case per state where the only CHIP-eligible member is FCEP-eligible, with expected premium 0.

Found in review of #10363. These states have no standard CHIP pregnancy pathway, so that PR's postpartum extension does not reach them; the issue already exists on main.