Unbuild orders with return subcontracting

When a transfer returning a subcontracted product is confirmed, Odoo automatically creates a draft unbuild order for that product. The unbuild is linked to the return transfer and marked as subcontracted, so it is kept separate from normal unbuild orders.

• The unbuild is created using the subcontractor's location as both source and destination, the product, quantity and bill of materials of the returned move, and the original manufacturing order when available.
• If the returned move is linked to more than one manufacturing order, Odoo blocks the operation with an error message.
• If the return transfer is set to immediate transfer (no planning), Odoo raises an error asking to use a planned transfer instead.
• When the return transfer is validated, any draft subcontracted unbuild orders linked to it are validated automatically, and their stock moves are dated just before the transfer's moves.
• The finished product moves from the unbuild are linked to the subcontracted moves of the transfer.
• A new menu 'Subcontracted Unbuild Orders' appears under the Manufacturing menu (visible only in debug mode) and lists only unbuild orders flagged as subcontracted. The standard Unbuild Orders list now hides subcontracted ones.
• The stock valuation report of the transfer also includes the valuation layers of the linked subcontracted unbuild orders.

The module extends mrp.unbuild, stock.move and stock.picking.