Refactor NJ tax aggregation variables to use parameter-driven lists

[hua7450]

Summary

Several NJ tax aggregation variables use hardcoded lists in Python, inconsistent with the pattern already used elsewhere in NJ (e.g., nj_additions, nj_gross_income) and other states (MD, NY) that use parameter files.

Variables Using Hardcoded Lists

Variable	Current Hardcoded List
nj_refundable_credits	nj_property_tax_credit, nj_eitc, nj_cdcc, nj_ctc
nj_total_exemptions	nj_regular_exemption, nj_senior_exemption, nj_dependents_exemption, nj_blind_or_disabled_exemption, nj_dependents_attending_college_exemption
nj_total_deductions	nj_medical_expense_deduction
nj_non_refundable_credits	(empty - should have parameter reference for consistency)

Variables Already Using Correct Pattern

• nj_additions → "gov.states.nj.tax.income.additions"
• nj_gross_income → "gov.states.nj.tax.income.gross_income_sources"
• nj_agi_subtractions → uses p.subtractions

Why This Matters

• PR Update New Jersey 2025 Individual Income Tax Model #7125 adds ANCHOR (2024) and Stay NJ (2026) credits that need proper effective dates
• No Python code changes needed when adding/removing items
• Enables proper historical accuracy
• Consistent with existing NJ patterns and other states

Checklist

• nj_refundable_credits → gov.states.nj.tax.income.credits.refundable
• nj_non_refundable_credits → gov.states.nj.tax.income.credits.non_refundable
• nj_total_exemptions → gov.states.nj.tax.income.exemptions.exemptions
• nj_total_deductions → gov.states.nj.tax.income.deductions.deductions