Add branching option to declare itemized deductions

[MaxGhenis]

Due to the AMT, some filers will be able to minimize tax liability by itemizing and declaring no itemized deductions. This will avoid the situation where marginal SALT increases taxes, as @PavelMakarchuk and I documented here.

Since the law does not require filers to list all possible itemized deductions, we should add a third branch option to capture this:

1. Take standard deduction
2. Take itemized deduction and maximize itemized deductions
3. Take itemized deduction and report zero itemized deductions

[MaxGhenis]

Actually itemizing with $0 itemized deductions won't be optimal, itemizing with $taxable_income itemized deductions is. We don't need to branch to do this; see https://github.com/PolicyEngine/policyengine-us/issues/5881