BUG: Product cloning retains source inventory links in CodebaseResource #601

Describe the bug
When cloning a product with both "Components, Packages, and Dependencies" (copy_inventory) and "Codebase resources" (copy_codebase_resources) checked, the cloned CodebaseResource still references the original product's ProductPackage and ProductComponent instead of the newly cloned ones.

In ProductCloneForm.save(), relations are duplicated using clone_related_objects(), which sets resource.product = target_product but leaves product_package_id and product_component_id pointing to the source product's records.

Because clone_related_objects() calls .save() directly, model validation is bypassed during the clone. But if someone later opens that cloned resource in Admin and clicks Save, Django blocks it with a validation error because CodebaseResource.clean() explicitly forbids linking packages/components from another product. Also, if the original product is ever deleted, these relations get set to NULL due to SET_NULL.

To Reproduce

1. Create a product (e.g. Product A 1.0.0).
2. Add a package to it (e.g. pkg:npm/left-pad@1.3.0).
3. Add a codebase resource (/src/index.js) to Product A and link its Product package field to that package.
4. Clone Product A with both copy_inventory and copy_codebase_resources enabled to create Product A 2.0.0 (copy).
5. Open the cloned codebase resource in Django Admin (/admin/product_portfolio/codebaseresource/<id>/change/).
6. Click Save without changing anything.
7. See validation error: pkg:npm/left-pad@1.3.0 is not available on Product A 2.0.0 (copy).

Expected behavior

• When both inventory and codebase resources are cloned, CodebaseResource.product_package and product_component should be remapped to the newly created cloned records on the target product.
• If codebase resources are cloned without inventory (copy_inventory unchecked), the cross-product package/component foreign keys should be cleared to keep the data clean.

Screenshots

1. Source product (Product A 1.0.0) with /src/index.js mapped to left-pad:

2. Cloned product (Product A 2.0.0 (copy)) created with both inventory and codebase resources:

3. Saving the cloned resource in Django Admin triggers clean() validation error:

Context (OS, Browser, Device, etc.):

• DejaCode: 6.0.0 (commit 8fc6013)
• OS: Windows
• Browser: Chrome
• Environment: Local Docker instance