Core Data: Optimize storage usage in ProductCategoryStore

[itsmeichigo]

Part of #14091

Description

This PR continues the optimization for the Core Data usage in the app by improving the usage in ProductCatgoryStore:

• Replaced the deprecated access to writerDerivedStorage with the new method performAndSave.
• Combine the deletion and upsertion when syncing the first page of categories.
• Move the deletion of unused categories to the background.
• Optimized fetch requests when upserting categories by fetching all categories at one.

Steps to reproduce

• Log in to a test store.
• Navigate to the Products tab and create a new product or open an existing one.
• Select Categories and confirm that the list is loaded successfully.
• Add a new category and confirm that it works as expected.
• Edit and delete the new category. Confirm that both work as expected.

Testing information

Tested on simulator iPhone 16 Pro iOS 18.0 and confirmed that:

• Category list loads correctly.
• Adding/Editing/Deleting categories work as expected.

Screenshots

N/A

---

• [ ] I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

TODO: @itsmeichigo to update the release notes before merging

Reviewer (or Author, in the case of optional code reviews):

Please make sure these conditions are met before approving the PR, or request changes if the PR needs improvement:

• [ ] The PR is small and has a clear, single focus, or a valid explanation is provided in the description. If needed, please request to split it into smaller PRs.
• [ ] Ensure Adequate Unit Test Coverage: The changes are reasonably covered by unit tests or an explanation is provided in the PR description.
• [ ] Manual Testing: The author listed all the tests they ran, including smoke tests when needed (e.g., for refactorings). The reviewer confirmed that the PR works as expected on all devices (phone/tablet) and no regressions are added.

[wpmobilebot]

📲 You can test the changes from this Pull Request in WooCommerce iOS by scanning the QR code below to install the corresponding build.

	App Name	WooCommerce iOS
	Build Number	pr14151-f0dc15b
	Version	20.8
	Bundle ID	com.automattic.alpha.woocommerce
	Commit	f0dc15bd423ad4571d707de078aa95389eb45529
	App Center Build	WooCommerce - Prototype Builds #11225

Automatticians: You can use our internal self-serve MC tool to give yourself access to App Center if needed.

[hafizrahman]

Testing note:

Tested in iPhone 15 Simulator with iOS 17.5 ✅ Edited an existing product, went to Categories and items were loaded properly ✅ Category creation worked correctly ✅ Category editing worked correctly ✅ Category deletion worked correctly