Add product sets in pickings

This module lets warehouse users add a predefined product set directly into a transfer (picking) instead of typing each product line by hand.

On a transfer form in draft state, a new "Add set" button appears in the header. Clicking it opens a small wizard where the user picks a product set and a quantity. The wizard shows the products contained in that set and, when confirmed, creates the corresponding stock move lines on the transfer with the chosen quantity applied to each set line.

Business rules shown in the code: - The button is only visible while the transfer is still in draft state. - The product set selection is filtered so that sets restricted to a specific partner are only offered when that partner matches the transfer's partner. - If a set is restricted to a partner and the transfer's partner is different, a validation error is raised saying the set is restricted for this user. - Move lines are created with the transfer's source and destination locations, partner, company, operation type, warehouse and the set line's sequence.

The module touches stock.picking (form view and move lines) and extends product.set.line and the product set wizard. It depends on the Inventory and Product Set modules.