Revise social security income taxation

This bill revises Montana's state income tax calculations by adjusting how federal taxable income is modified to determine state taxable income. It directly affects Montana residents who file state income tax returns, particularly those with complex federal tax situations involving investments, retirement accounts, or business income. The key provision adds certain federal deductions back to income for state tax purposes while subtracting specific Montana-exempt items like interest on U.S. government bonds and military salaries. The bill also clarifies how withdrawals from savings accounts for medical, education, or home purchase purposes are treated differently depending on whether they are used for eligible expenses.