Prevent NY filers from claiming both college tuition credit and deduction

From https://www.nysenate.gov/legislation/laws/TAX/615 (d)(4) on the college tuition itemized deduction:

> Provided, however, no deduction shall be allowed under this paragraph to a taxpayer who claims the credit provided under subsection (t) of section six hundred six of this article.

And https://www.nysenate.gov/legislation/laws/TAX/606 (t)(4) on the credit:

>(6) Limitation. No credit shall be allowed under this subsection to a taxpayer who claims the itemized deduction provided under paragraph four of subdivision (d) of section six hundred fifteen of this article.

We currently approximate this by only allowing the credit for non-itemizers. Proper modeling will require branching so low priority given the computational complexity.

Start by reviewing the existing approximation that allows the college tuition credit only for non-itemizers, then compare it with the NY Tax Law provisions cited in the issue. Done means the model prevents a taxpayer from claiming both the college tuition credit and the itemized deduction, rather than relying on the current approximation.

Written by the indexing model from the issue text.