Product Supplierinfo for Customers and Product Supplierinfo Group compatibility

This is a technical compatibility module that installs automatically when both the customer supplier info and supplier info group modules are present. It does not add new menus or screens for users.

What it changes: - It restores the standard field definitions on the product.customerinfo model, which stores customer-specific product details such as vendor, product name, product code, sequence and company. - It makes the group_id field optional again, so customer product records do not require a supplier info group. - It sets sensible defaults: the company defaults to the current company, and the sequence defaults to 1. - It ensures the vendor, product template and product variant fields keep their normal behaviour, including company checks and deletion rules. - When a new customer product record is created, it is saved with a special context that skips group-specific logic, avoiding errors caused by the grouping module.

Because of this, users can keep using customer-specific product references and prices in sales without the grouping module breaking those records. The module touches the product.customerinfo model and depends on product_supplierinfo_for_customer and product_supplierinfo_group.