Core Data Stack updates

[itsmeichigo]

Closes: #14054
Also closes: #2370

Description

This PR adds a few improvements to the Core Data stack:

• Updated the writerDerivedStorage to be independent of the main context. Instead, the background context is now directly associated with the persistent container following Apple's recommendation. The main context now merges changes from the persistent container automatically.
• A writer operation queue has been introduced to take care of write operations one-by-one following WP/JP's implementation here. I'm following the simple variation for the completion handler without the result parameter as we don't currently have any failure handling for the write operations - I suppose we can add that variation when we need it.
• Removed the unused method performBackgroundTask - we want to avoid creating too many background context through this method.
• Updated saveDerivedType to only save the background context to the persistent container.
• Marked access to writerDerivedStorage and saveDerivedType as deprecated and added a helper method performAndSave for performing write operations similarly to WP/JP's Core Data stack. Updates for the stores will be handled in future PRs.
• Added check to ensure write operations are handled in a background context. The checks are handled in debug mode only, and a new launch argument -enforce-core-data-write-in-background has been added to enable assert when writing is done on the main context.
• Initialize the storage manager along with AppDelegate to ensure that the Core Data stack is created before the stores manager. This is an attempt to eliminate confusing stack traces [peaMlT-Rx-p2#comment-2194]. The order of initialization should now be as follows: CrashLogging > CoreDataManager > DefaultStoresManager.
• Keep product's date and dateCreated Swift properties optional to avoid crashes when transforming deleted product objects in Core Data.

TODO: @itsmeichigo to update the release notes before merging.

Steps to reproduce

Smoke testing the app

• With -enforce-core-data-write-in-background disabled, build and run the app in debug mode.
• Log in to a test store with existing products/orders/Blaze campaigns.
• Smoke test the app following the guide P91TBi-bVe-p2.

Testing enforcing write in background

• With -enforce-core-data-write-in-background enabled, build and run the app in debug mode.
• Log in to a test store with existing products/orders/Blaze campaigns.
• Confirm that the assert causes a fatal error where a write operation is handled in the main context.

Testing information

Tested on device iPad pro 4th gen iOS 17.6:

• Logged in to an atomic store with wpcom account successfully.
• Confirmed that dashboard works as before: stats cards with different time ranges, all cards enabled with different filters.
• Confirmed that orders work normally: pagination, searching, order creation and edit, creating shipping labels, marking orders as complete.
• Confirmed that products work normally: pagination, searching, bulk update, product creation with AI, creating & editing variable products, updating product details.
• Confirmed that hub menu works normally: store switching, settings, payments, google ads, blaze, woo admin, view store, coupons, reviews, inbox, customers.

Tested on simulator iPhone 15 Pro iOS 17.4 and -enforce-core-data-write-in-background enabled and confirmed that write operations in the main context causes assertion failure.

Screenshots

N/A

---

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

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	pr14013-64c71ce
	Version	20.7
	Bundle ID	com.automattic.alpha.woocommerce
	Commit	64c71ce
	App Center Build	WooCommerce - Prototype Builds #11135

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

[wpmobilebot]

Version 20.6 has now entered code-freeze, so the milestone of this PR has been updated to 20.7.

[itsmeichigo]

Moved the milestone to 20.8 to avoid causing any issue during the Woo DM. Other PRs will be based on top of this PR and merged gradually after this PR is merged.

[dangermattic]

	1 Warning
⚠️	This PR is assigned to the milestone 20.8. The due date for this milestone has already passed. Please assign it to a milestone with a later deadline or check whether the release for this milestone has already been finished.

Generated by 🚫 Danger

[selanthiraiyan]

Thanks for working on this, Huong! 👏

The changes LGTM, and it works well on an iPhone simulator running iOS 17.4.

I left a few non-blocking suggestions and questions.

[itsmeichigo]

Thanks @selanthiraiyan for the reviews! I responded to your comments regarding the unit tests, let me know what you think. I'll merge the PR once I get another green light from you.

[selanthiraiyan]

Thanks for the updates and comments, Huong! Let us merge this PR. 🚢