Purchase Invoice Status Partial

This module extends the purchase order invoicing status with an extra option called 'Partially Invoiced'. It is useful when a vendor has billed only part of what was ordered and some goods have already been received.

• The status is calculated automatically for purchase orders that are in the 'Purchase Order' or 'Locked' state.
• It appears when three conditions are met at the same time: some quantity has already been invoiced, that invoiced quantity is still lower than the total ordered quantity, and at least some quantity has been received.
• The calculation looks at the order lines, ignoring section and note lines, and uses the product unit of measure precision to decide whether a quantity counts as zero.
• In the purchase orders list view, orders with this status are highlighted with a warning colour, making them easy to spot.
• The module only touches the purchase order model and its list view; it does not add new menus or screens of its own.

Because the status is computed, it updates automatically as invoices and receipts are recorded, without any manual action from the user.