This commit introduces a new `tax.js` module containing functions for tax rate resolution and amount calculation with tax. The `amountWithTax` and `resolveTaxRate` functions are integrated into various schemas, including `invoice`, `orderitem`, `shipment`, `courierservice`, `filament`, `part`, and `product`, enhancing their ability to compute amounts with applicable taxes. Additionally, corresponding tests are added to ensure the correctness of the new tax-related functionalities.
