Fix parent product price cleared when variant price is changed

[Copilot]

Changing a variant's price overwrites the parent product's price/VAT to 0. Root cause: clone on a Doctrine-managed ProductStoreValues entity preserves the id, so persisting the "new" variant entity actually updates the parent's DB record.

Replace clone with factory-created instances in both code paths:

• preSetData (admin form path): New blank entity via getFactory()->createNew(). The Symfony form submission immediately populates all fields (store, price, taxRule, unitDefinitionPrices), so no property copying needed.
• save (programmatic path): New entity via factory with explicit copy of store, price, and taxRule from the inherited entity before persist.

// Before: clone retains the parent's Doctrine identity
$productStoreValue = clone $productStoreValue;

// After: fresh entity gets its own INSERT instead of UPDATE on parent
$newStoreValue = $this->getFactory()->createNew();
$newStoreValue->setStore($productStoreValue->getStore());
$newStoreValue->setPrice($productStoreValue->getPrice());
$newStoreValue->setTaxRule($productStoreValue->getTaxRule());

Regression of #1486, previously patched in #1491 for CoreShop 2.2.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Price and VAT are cleared on parent product when price of new created variant is changed</issue_title>
<issue_description>Steps to reproduce:

• Add a product and set its price
• On CoreShopProduct set "allowInherit" and "allowVariants" to true
• Add a product variant and change its price
• The price of parent product will be set to 0

This appears to be a regression of #1486
This patch fixed the issue previously in CoreShop 2.2: https://github.com/coreshop/CoreShop/pull/1491/files

In the current version I've replaced the $storeValuesEntity = clone $storeValuesEntity; with $storeValuesEntity = new ProductStoreValues() and it seems to work correctly in my local environment. However, I don’t fully understand why "clone" doesn't work as expected.
I’m also not sure what the consequences might be if a completely new ProductStoreValues instance is created.

I can create a PR if my changes make sense.</issue_description>

Comments on the Issue (you are @copilot in this section)

@dpfaffenbauer @80Quattro please create a PR and lets see if the tests still run

• Fixes Price and VAT are cleared on parent product when price of new created variant is changed #2973

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Quality Gate passed

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